Field-induced transition within the superconducting state of CeRh2As2

Materials with multiple superconducting phases are rare. Here, we report the discovery of two-phase unconventional superconductivity in CeRh₂As₂ Using thermodynamic probes, we establish that the superconducting critical field of its high-field phase is as high as 14 tesla, even though the transition temperature is only 0.26 kelvin. Furthermore, a transition between two different superconducting phases is observed in a c axis magnetic field. Local inversion-symmetry breaking at the cerium sites enables Rashba spin-orbit coupling alternating between the cerium sublayers. The staggered Rashba coupling introduces a layer degree of freedom to which the field-induced transition and high critical field seen in experiment are likely related.

Origin of the quasi-quantized Hall effect in ZrTe5

The quantum Hall effect (QHE) is traditionally considered to be a purely two-dimensional (2D) phenomenon. Recently, however, a three-dimensional (3D) version of the QHE was reported in the Dirac semimetal ZrTe5. It was proposed to arise from a magnetic-field-driven Fermi surface instability, transforming the original 3D electron system into a stack of 2D sheets. Here, we report thermodynamic, spectroscopic, thermoelectric and charge transport measurements on such ZrTe5 samples. The measured properties: magnetization, ultrasound propagation, scanning tunneling spectroscopy, and Raman spectroscopy, show no signatures of a Fermi surface instability, consistent with in-field single crystal X-ray diffraction. Instead, a direct comparison of the experimental data with linear response calculations based on an effective 3D Dirac Hamiltonian suggests that the quasi-quantization of the observed Hall response emerges from the interplay of the intrinsic properties of the ZrTe5 electronic structure and its Dirac-type semi-metallic character.

Negative Thermal Expansion in the Plateau State of a Magnetically Frustrated Spinel

We report on negative thermal expansion (NTE) in the high-field, half-magnetization plateau phase of the frustrated magnetic insulator CdCr_{2}O_{4}. Using dilatometry, we precisely map the phase diagram at fields of up to 30 T and identify a strong NTE associated with the collinear half-magnetization plateau for B>27  T. The resulting phase diagram is compared with a microscopic theory for spin-lattice coupling, and the origin of the NTE is identified as a large negative change in magnetization with temperature, coming from a nearly localized band of spin excitations in the plateau phase. These results provide useful guidelines for the discovery of new NTE materials.

Cascade of Magnetic-Field-Induced Lifshitz Transitions in the Ferromagnetic Kondo Lattice Material YbNi_{4}P_{2}

A ferromagnetic quantum critical point is thought not to exist in two- and three-dimensional metallic systems yet is realized in the Kondo lattice compound YbNi_{4}(P,As)_{2}, possibly due to its one-dimensionality. It is crucial to investigate the dimensionality of the Fermi surface of YbNi_{4}P_{2} experimentally, but common probes such as angle-resolved photoemission spectroscopy and quantum oscillation measurements are lacking. Here, we study the magnetic-field dependence of transport and thermodynamic properties of YbNi_{4}P_{2}. The Kondo effect is continuously suppressed, and additionally we identify nine Lifshitz transitions between 0.4 and 18 T. We analyze the transport coefficients in detail and identify the type of Lifshitz transitions as neck or void type to gain information on the Fermi surface of YbNi_{4}P_{2}. The large number of Lifshitz transitions observed within this small energy window is unprecedented and results from the particular flat renormalized band structure with strong 4f-electron character shaped by the Kondo lattice effect.

The world's smallest capacitive dilatometer, for high-resolution thermal expansion and magnetostriction in high magnetic fields

For the characterization of novel quantum phases of matter, it is often required to study materials under multi-extreme conditions, in particular down to very low temperatures and in very high magnetic fields. We developed the world's smallest high-resolution capacitive dilatometer suitable for temperatures down to 10 mK and usage in high magnetic fields up to 37.5 T. Despite the extreme miniaturization, the capacitive dilatometer can resolve length changes down to 0.01 Å. This is an unprecedented resolution in a capacitive dilatometer of this compact size. Many cryogenic devices have limited space. Due to the extremely reduced cell size (3 cm³, 12 g), implementation or new applications in many of these sample space lacking devices are now possible. As an important example, the minute device can now be rotated in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system. The present super compact design provides also for high resolution thermal expansion and magnetostriction measurements in a 15.2 mm diameter tube, enabling its use in the 32 mm bore, 37.5 T Bitter magnet at the High Field Magnet Laboratory in Nijmegen down to a temperature of 300 mK.

A uniaxial stress capacitive dilatometer for high-resolution thermal expansion and magnetostriction under multiextreme conditions

Thermal expansion and magnetostriction are directional dependent thermodynamic quantities. For the characterization of novel quantum phases of matter, it is required to study materials under multi-extreme conditions, in particular, down to very low temperatures, in very high magnetic fields or under high pressure. We developed a miniaturized capacitive dilatometer suitable for temperatures down to 20 mK and usage in high magnetic fields, which exerts a large spring force between 40 to 75 N on the sample. This corresponds to a uniaxial stress up to 3 kbar for a sample with cross section of (0.5 mm)(2). We describe design and performance test of the dilatometer which resolves length changes with high resolution of 0.02 Å at low temperatures. The miniaturized device can be utilized in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system.

Paneth cell α-defensin 6 (HD-6) is an antimicrobial peptide

Defensins protect human barriers from commensal and pathogenic microorganisms. Human α-defensin 6 (HD-6) is produced exclusively by small intestinal Paneth cells but, in contrast to other antimicrobial peptides (AMPs) for HD-6, no direct antibacterial killing activity has been detected so far. Herein, we systematically tested how environmental factors, like pH and reducing conditions, affect antimicrobial activity of different defensins against anaerobic bacteria of the human intestinal microbiota. Remarkably, by mimicking the intestinal milieu we detected for the first time antibacterial activity of HD-6. Activity was observed against anaerobic gut commensals but not against some pathogenic strains. Antibiotic activity was attributable to the reduced peptide and independent of free cysteines or a conserved histidine residue. Furthermore, the oxidoreductase thioredoxin, which is also expressed in Paneth cells, is able to reduce a truncated physiological variant of HD-6. Ultrastructural analyses revealed that reduced HD-6 causes disintegration of cytoplasmic structures and alterations in the bacterial cell envelope, while maintaining extracellular net-like structures. We conclude that HD-6 is an antimicrobial peptide. Our data suggest two distinct antimicrobial mechanisms by one peptide: HD-6 kills specific microbes depending on the local environmental conditions, whereas known microbial trapping by extracellular net structures is independent of the reducing milieu.

k=0 magnetic structure and absence of ferroelectricity in SmFeO3

SmFeO3 has attracted considerable attention very recently due to its reported multiferroic properties above room temperature. We have performed powder and single crystal neutron diffraction as well as complementary polarization dependent soft X-ray absorption spectroscopy measurements on floating-zone grown SmFeO3 single crystals in order to determine its magnetic structure. We found a k=0 G-type collinear antiferromagnetic structure that is not compatible with inverse Dzyaloshinskii-Moriya interaction driven ferroelectricity. While the structural data reveal a clear sign for magneto-elastic coupling at the Néel-temperature of ∼675  K, the dielectric measurements remain silent as far as ferroelectricity is concerned.

Thermodynamic evidence for valley-dependent density of states in bulk bismuth

Electron-like carriers in bismuth are described by the Dirac Hamiltonian, with a band mass becoming a thousandth of the bare electron mass along one crystalline axis. The existence of three anisotropic valleys offers electrons an additional degree of freedom, a subject of recent attention. Here, we map the Landau spectrum by angle-resolved magnetostriction, and quantify the carrier number in each valley: while the electron valleys keep identical spectra, they substantially differ in their density of states at the Fermi level. Thus, the electron fluid does not keep the rotational symmetry of the lattice at low temperature and high magnetic field, even in the absence of internal strain. This effect, reminiscent of the Coulomb pseudogap in localized electronic states, affects only electrons in the immediate vicinity of the Fermi level. It presents the most striking departure from the non-interacting picture of electrons in bulk bismuth.

A compact and miniaturized high resolution capacitance dilatometer for measuring thermal expansion and magnetostriction

We describe the design, construction, calibration, and two different applications of a miniature capacitance dilatometer. The device is suitable for thermal expansion and magnetostriction measurements from 300 K down to about 25 mK, with a resolution of 0.02 Å at low temperatures. The main body of the dilatometer is fabricated from a single block of a Be-Cu alloy by electrical discharge milling. This creates an extremely compact high-resolution measuring cell. We have successfully tested and operated dilatometers of this new type with the commonly used physical property measurement system by quantum design, as well as with several other cryogenic refrigeration systems down to 25 mK and in magnetic fields up to 20 T. Here, the capacitance is measured with a commercially available capacitance bridge. Using a piezoelectric rotator from Attocube Systems, the cell can be rotated at T = 25 mK inside of an inner vacuum chamber of 40 mm diameter. The miniaturized design for the one-axis rotation setup allows a rotation of 360°.

Kondo-cluster-glass state near a ferromagnetic quantum phase transition

We report on a comprehensive study of CePd(1-x)Rh(x) (0.6 <or= x <or= 0.95) poly- and single crystals close to the ferromagnetic instability by means of low-temperature ac susceptibility, magnetization, and volume thermal expansion. The signature of ferromagnetism in this heavy-fermion system can be traced from 6.6 K in CePd down to 25 mK for x = 0.87. Despite pronounced non-Fermi-liquid effects in both specific heat and thermal expansion, the Grüneisen ratio does not diverge as T --> 0, providing evidence for the absence of a quantum critical point. Instead, a peculiar "Kondo-cluster-glass" state is found for x >or= 0.65, and the non-Fermi-liquid effects in the specific heat, ac susceptibility, and magnetization are compatible with the quantum Griffiths phase scenario.

Quantum criticality in the cubic heavy-fermion system CeIn3-xSnx

We report a comprehensive study of CeIn3-xSnx (0.55<or=x< or=0.8) single crystals close to the antiferromagnetic quantum-critical point (QCP) at xc approximately 0.37 by means of the low-temperature thermal expansion and Grüneisen parameter. This system represents the first example for a cubic heavy fermion in which TN can be suppressed continuously down to T=0. A characteristic sign change of the Grüneisen parameter between the antiferromagnetic and paramagnetic states indicates the accumulation of entropy close to the QCP. The observed quantum-critical behavior is compatible with the predictions of the itinerant theory for three-dimensional critical spin fluctuations. This has important implications for the role of the dimensionality in heavy-fermion QCPs.

Silver ion dynamics in silver borate glasses: spectra and multiple-time correlation functions from 109Ag-NMR

The motion of silver ions in (AgI)x-(Ag2O-B2O3)1-x glasses with AgI concentrations of x=0.5 and 0.7 was studied using 109Ag-NMR. The NMR spectra were analyzed in terms of a superposition of two different contributions. These are associated with Ag ions, which hop on vastly different time scales. The existence of dynamic heterogeneity, i.e. the existence of slow and of fast contributions to the hopping dynamics was directly demonstrated using a four-time stimulated-echo experiment. The results are compatible with an intrinsically exponential response. From measurements of the spectra and of two-time correlation functions a Gaussian distribution of energy barriers, hindering the ionic motion, could be mapped out.

Grüneisen ratio divergence at the quantum critical point in CeCu(6-x)Agx

The heavy-fermion system CeCu6-xAgx is studied at its antiferromagnetic quantum critical point, xc=0.2, by low-temperature (T> or =50 mK) specific heat, C(T), and volume thermal expansion, beta(T), measurements. Whereas C/T proportional to log((T0/T) would be compatible with the predictions of the itinerant spin-density-wave (SDW) theory for two-dimensional critical spin fluctuations, beta(T)/T and the Grüneisen ratio, Gamma(T) proportional to beta/C, diverge much weaker than expected, in strong contrast to this model. Both C and beta, plotted as a function of the reduced temperature t=T/T0 with T0=4.6 K, are similar to what was observed for YbRh2(Si(0.95)Ge(0.05))2 (T0=23.3 K), indicating a striking discrepancy to the SDW prediction in both systems.

Nature of the A phase in CeCu2Si2

Neutron diffraction experiments have been performed on a magnetically ordered CeCu2Si2 single crystal exhibiting A-phase anomalies in specific heat and thermal expansion. Below T(N) approximately 0.8 K antiferromagnetic superstructure peaks have been detected. The propagation vector of the magnetic order appears to be determined by the topology of the Fermi surface of heavy quasiparticles as indicated by renormalized band-structure calculations. The observation of long-range incommensurate antiferromagnetic order as the nature of the A phase in CeCu2Si2 suggests that a spin-density-wave instability is the origin of the quantum critical point in CeCu2Si2.

Divergence of the grüneisen ratio at quantum critical points in heavy fermion metals

We present low-temperature volume thermal expansion, beta, and specific heat, C, measurements on high-quality single crystals of CeNi2Ge2 and YbRh2(Si0.95Ge0.05)(2) which are located very near to quantum critical points. For both systems, beta shows a more singular temperature dependence than C, and thus the Grüneisen ratio Gamma proportional to beta/C diverges as T-->0. For CeNi2Ge2, our results are in accordance with the spin-density wave (SDW) scenario for three-dimensional critical spin fluctuations. By contrast, the observed singularity in YbRh2(Si0.95Ge0.05)(2) cannot be explained by the itinerant SDW theory but is qualitatively consistent with a locally quantum critical picture.

[Percutaneous revascularization of multivessel coronary disease using stents - a multicenter, prospective study]

BACKGROUND AND OBJECTIVE

Symptomatic patients with multivessel coronary disease (MVD) benefit from both coronary artery bypass grafting (CABG) and percutaneous coronary angioplasty (PTCA). The >>German Angioplasty Bypass Investigation<< (GABI-I) trial randomized patients to one of these treatment strategies between 1986 and 1991. In order to evaluate the impact of current technology, in particular coronary stents, the GABI-II trial was initiated, which in 1996 and 1997 prospectively enrolled patients according to the initial GABI-I criteria.

PATIENTS AND METHODS

Into the study 136 consecutive patients (108 men, 28 women; 63 +/- 12 years) were included. Patients from GABI-I served as controls.

RESULTS

A mean of 2.1 +/- 0.5 vessels were treated per patient (vs. 1.9 +/- 0.5 vessels in the PTCA arm of GABI-I) and 63 % of the lesions were covered with stents. With respect to the primary endpoint less patients remained with a CCS class III or IV in GABI-II after 12 months (1,5 % vs. 8 % in the PTCA arm of GABI-I, p<0,01). No patient required emergency or urgent bypass operation in GABI-II (vs. 9 % in GABI-I, p < 0.01). After 12 months, 8 % of the patients were sent for bypass surgery (CABG) vs. 21 % in GABI-I (p < 0.001), and 20 % (vs. 23 % in GABI-I) of the patients underwent Re-PTCA. The percentage of patients without reinterventions was 72 % vs. 56 % in GABI-I (p < 0.01), but remained lower compared to patients randomized to CABG in GABI-I (94 %, p < 0.001).

CONCLUSION

PTCA in patients with MVD is still associated with a higher reintervention rate as compared with CABG. However, in contrast to angioplasty a decade ago, PTCA in conjunction with stents significantly lowered the need for subsequent revascularization, which was mainly driven by the reduced necessity for bypass surgery.

A randomized comparison of balloon angioplasty versus rotational atherectomy in complex coronary lesions (COBRA study)

AIMS

Rotablation is a widely used technique for the treatment of complex coronary artery lesions but is so far only poorly supported by controlled studies. The Comparison of Balloon-Angioplasty versus Rotational Atherectomy study (COBRA) is a multicentre, prospective, randomized trial to compare short- and long-term effects of percutaneous transluminal coronary angioplasty (PTCA) and rotablation in patients with angiographically pre-defined complex coronary artery lesions.

METHODS AND RESULTS

At seven clinical sites 502 patients with pre-defined complex coronary artery lesions were assigned to either PTCA (n=250) or rotablation (n=252). Primary end-points were procedural success, 6-month restenosis rates in the treated segments, and major cardiac events during follow-up. Procedural success was achieved in 78% (PTCA), and 85% (rotablation) (P=0.038) of cases. Crossover from PTCA to rotablation was 4% and 10% vice versa (P=0.019). There was no difference between PTCA and rotablation with respect to procedure-related complications such as Q wave infarctions (2.4% each), emergency bypass surgery (1.2% versus 2.4%), and death (1.6% versus 0.4%). However, more stents were required after PTCA (14.9% versus 6.4%, P<0.002), predominantly for bailout or unsatisfactory results. Including bail-out stents as an end-point, the procedural success rates were 73% for angioplasty and 84% for rotablation (P=0.006). At 6 months, symptomatic outcome, target vessel reinterventions and restenosis rates (PTCA 51% versus rotablation 49%, P=0.33) were not different.

CONCLUSION

Complex coronary artery lesions can be treated with a high level of success and low complication rates either by PTCA with adjunctive stenting or rotablation. The long-term clinical and angiographic outcome is comparable.

[An acute septic course of melioidosis after a stay in Thailand]

HISTORY AND CLINICAL FINDINGS

Two weeks after returning from a trip to Thailand a 79-year-old man developed a higher fever, pain in the right flank and progressive clouding of consciousness. She had meningism on admission.

INVESTIGATIONS

There was a marked leukocytosis (WBC count 17,700/microliter) and raised C-reactive protein (6.5 mg/dl). Cerebrospinal fluid was clear, containing 119 cells/mm3 and elevated protein (90 mg/dl). Abdominal sonography demonstrated segmental pyelonephritis, and blood culture grew Pseudomonas pseudomallei.

TREATMENT AND COURSE

On the basis of sensitivity tests imipenem was chosen as the antibiotic and was given for 6 weeks. Because of an inadequate response and a right renal abscess a right nephrectomy was performed. After marked improvement the septicaemia recurred one week after antibiotic treatment had been discontinued, and the patient died.

CONCLUSION

Efficacious treatment of melioidosis (a glanders-like disease) presupposes diagnosis of the causative microorganism and testing of its antibiotic sensitivity. As Pseud. pseudomallei may encapsulate and persist intracellularly, the selection of antibiotic and the duration of treatment are crucial.

[Reliability of bacteriologic diagnosis of tuberculosis. Results of external quality control 1991-1992]

A report on the results of three proficiency-tests is presented. They were performed to test the efficiency of mycobacteriological laboratories. The incidence of false test-results varied between samples from 2 to 20%. In each survey between 10 and 20% of the participating laboratories arrived at unacceptably poor total assessments. The proportion of institutes where lack of expert competence can be suspected due to repeated failure in external quality tests, was between 3% (microscopy) and 13% (differentiation between tuberculosis bacteria and environmental mycobacteria). Reproducibility of good and poor total assessments in more than 80% of the laboratories indicates even if a laboratory participates in a survey only once, this will already supply quite reliable information on the efficiency of that laboratory. Even though many laboratories with poor performance in surveys try to improve their standards on their own, it is evident from the large number of institutes with repeated poor results, as well as from the irregular participation by many institutes in external quality tests, that external quality assurance of bacterio-logical tuberculosis diagnostics cannot be achieved by proficiency tests alone. Since the provisions of the Federal law on epidemics do not bestow sufficient legal competence on the health authorities in respect of control of the laboratories, and also because eventual sanctions imposed by the sickness insurance bodies cannot be effective in all cases, it is at present imperative that treating physicians take particularly great interest in the efficiency of the laboratories commissioned by them, for their patients' sake.

Computer-assisted identification of mycobacteria using code lists--results of a multi-centric study. German Working Group on Mycobacteria

The frequency of isolation of environmental mycobacteria from clinical specimens has increased significantly in the course of the last years. Assessment of the medical importance of such isolates always depends on a correct identification of any of these strains. In a multicentric study, the efficacy of a standardized, computer-aided system for identification has been evaluated. 13 Laboratories received 24 strains of mycobacteria each and were asked to test all these strains for 16 different features. The results were coded in a standardized way. For the evaluation of these tests, the laboratories were supplied with a list containing all possible codes, which might be indicative of one or another identification. The results proved the logic of the approach. However, the application of the system lead to a correct identification in only 74% of all attempts. It is concluded that such a standardized approach is not useful for mycobacteria, because it requires too much working time and material. It will be more practical to concentrate on a smaller number of tests in the peripheral laboratories, which might allow the identification of M. tuberculosis and a few other species and to leave the definitive identification to reference laboratories. The development of faster, simpler and more reliable methods remains highly desirable.

[Further experiences with ovum lavage with respect to preventing premature labor]

Between January and December 1990, lavage of the ovum was performed in 64 gravidae with actual or potential symptoms of premature labour. Subsequently the lavage fluid was microbiologically examined. The present study discusses the indications for this new method, how it is performed and the results obtained. Microorganisms possibly necessitating treatment were detected in the lavage fluid of 30 (47%) of the gravidae at risk. Thirty-nine patients manifested actual symptoms of imminent premature birth, such as labour or critical cervical status. Results of fluid tests were positive in 23 (59%) of these patients, while according to the results of conventional cervical or vaginal smear tests performed simultaneously, treatment was necessary in only 13% of them. The majority of the microorganisms in the lavage fluid (coagulase-negative, haemolytic and group D streptococci were usually detected) are only facultatively pathogenic and are found in small quantities in cervical smears as normal "local flora". The mean delivery date was in gestational week (GW) 37/1, and for patients with antibiosis produced by a suitable antibiotic in GW 38/3 (10 weeks after lavage was performed). In view of the results of this study, bacteriological testing of ovum lavage fluid may be regarded as a useful complementary method for detecting ascending infections. It may advance pathogenetic research into late abortion and premature birth and further reduce the premature birth rate.

[High dose intensity with COP-BLAM in Hodgkin's disease with unfavorable risk factors]

Thirty three patients with unfavourable risk factors suffering from Hodgkin's disease received COPBlAM polychemotherapy as first treatment in a phase-II study between 3/86 and 2/89. The median cumulative relative dose intensity (RDI) of 0.97, calculated as a measure for the given amount of cytostatics per time, was very high. Fourteen patients (43%) achieved a complete remission (CR); 11 (33%) additional cases were categorized as far-reaching remission (FRR) due to small residual tumors in the regions of originally large tumor masses, 7 (21%) as partial remission (PR), and one case (3%) as progression. As the small residual tumors of the patients grouped as FRR did not shrink during the following radiotherapy (RT), these cases were also classified as complete responders retrospectively. Thus, after chemotherapy 76% CR resulted. After completion of RT 91% of the patients have achieved a CR. The progress-free survival probability and the survival probability were 83% and 86% respectively after 45 months.

[Non-hematologic toxicity in high-dose cytarabine therapy]

The hence reported non-haematologic toxicity in high-dose cytarabin mainly concerned CNS (cerebellar dysfunction), eyes (keratitis and conjunctivitis), skin (erythema), and gastrointestinal tract (vomiting, diarrhea). It partly depends on dosage and partly on duration of treatment. A dose of 48 g/sq m within one cycle apparently represents a critical upper limit as hence especially the risk of irreversible brain damage increases. Considering the fact that the indication for high-dose cytarabin is given mainly for poor prognostic failures and relapses in acute leukemias toxicity seems to be acceptable.

[A comparison of antibiotic resistance patterns and pyocine types between strains of Pseudomonas aeruginosa from animal and human sources (author's transl)]

291 strains of Pseudomonas aeruginosa from human bacteriological samples were compared with 102 strains which had been isolated from animals for frequency of pyocine-types and patterns of antibiotic resistance. 146 strains had been isolated from hospitalized patients and 145 from out-patients. More strains of animal origin were sensitive to carbenicillin and tetracyclines compared to strains of human origin. Since the frequency of different pyocine-types is the same in all three groups, it is concluded, that antibiotic resistance may be transferred from man to animal and vice versa via transfer of Pseudomonas aeruginosa.

[Comparative pyocine typing of Pseudomonas aeruginosa with different indicator sets (author's transl)]

In a comparative study, 336 strains of Ps. aeruginosa were typed by their pyocine production with the indicator-sets of Gillies and Govan, Govan and Gillies, and with the author's set. The results obtained by either of the three sets of indicators showed a high degree of correlation with the results obtained by means of other sets. These correlations allow a subdivision of strains of Pseudomonas aeruginosa into four major subgroups. The possible reasons for the existence of such subgroups and for the correlations between pyocine types and serological groups, which have been demonstrated by other authors, are discussed. For practical purposes and epidemiological investigations the advantages of combined pyocine typing with different sets of indicators are discussed, and a combination of the indicators of Govan and Gillies with the author's set is recommended, giving the most even distribution of epidemiologically unrelated strains of Ps. aeruginosa among different pyocine types with the smallest possible number of indicators.