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Stankiewicz J, Schlottmann P, Arauzo A, Martinez Perez MJ, Rosa PFS, Civale L, Fisk Z. Localized magnetic moments in metallic SrB 6 single crystals. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:065602. [PMID: 30524054 DOI: 10.1088/1361-648x/aaf40f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The specific heat [Formula: see text] of metallic SrB6 single crystals shows an anomalous behavior for [Formula: see text] K which varies strongly with an applied magnetic field. This is consistent with a two-level Schottky system. We ascribe the excess of [Formula: see text] in this temperature range to localized magnetic moments. In addition, features that are attributable to a partial ferromagnetic polarization of a conduction electron gas are observed. These results are supported by magnetization measurements and are compatible with the transport properties reported previously (Stankiewicz 2016 Phys. Rev. B 94 125141).
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Affiliation(s)
- Jolanta Stankiewicz
- Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, 50009-Zaragoza, Spain
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2
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Gan LY, Wang R, Jin YJ, Ling DB, Zhao JZ, Xu WP, Liu JF, Xu H. Emergence of topological nodal loops in alkaline-earth hexaborides XB6(X = Ca, Sr, and Ba) under pressure. Phys Chem Chem Phys 2017; 19:8210-8215. [DOI: 10.1039/c6cp08421d] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Based on first-principles calculations, we report that external pressure can induce a topological phase transition in alkaline-earth hexaborides, XB6(X = Ca, Sr, and Ba).
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Affiliation(s)
- L.-Y. Gan
- Department of Physics
- South University of Science and Technology of China
- Shenzhen 518055
- China
- Key Laboratory of Advanced Technology of Materials (Ministry of Education)
| | - R. Wang
- Department of Physics
- South University of Science and Technology of China
- Shenzhen 518055
- China
- Institute for Structure and Function & Department of Physics
| | - Y. J. Jin
- Department of Physics
- South University of Science and Technology of China
- Shenzhen 518055
- China
| | - D. B. Ling
- Department of Physics
- Anhui University
- Hefei 230601
- China
| | - J. Z. Zhao
- Department of Physics
- South University of Science and Technology of China
- Shenzhen 518055
- China
| | - W. P. Xu
- Department of Physics
- South University of Science and Technology of China
- Shenzhen 518055
- China
| | - J. F. Liu
- Department of Physics
- South University of Science and Technology of China
- Shenzhen 518055
- China
| | - H. Xu
- Department of Physics
- South University of Science and Technology of China
- Shenzhen 518055
- China
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Kang CJ, Denlinger JD, Allen JW, Min CH, Reinert F, Kang BY, Cho BK, Kang JS, Shim JH, Min BI. Electronic Structure of YbB_{6}: Is it a Topological Insulator or Not? PHYSICAL REVIEW LETTERS 2016; 116:116401. [PMID: 27035312 DOI: 10.1103/physrevlett.116.116401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2015] [Indexed: 06/05/2023]
Abstract
To finally resolve the controversial issue of whether or not the electronic structure of YbB_{6} is nontrivially topological, we have made a combined study using angle-resolved photoemission spectroscopy (ARPES) of the nonpolar (110) surface and density functional theory (DFT). The flat-band conditions of the (110) ARPES avoid the strong band bending effects of the polar (001) surface and definitively show that YbB_{6} has a topologically trivial B 2p-Yb 5d semiconductor band gap of ∼0.3 eV. Accurate determination of the low energy band topology in DFT requires the use of a modified Becke-Johnson exchange potential incorporating spin-orbit coupling and an on-site Yb 4f Coulomb interaction U as large as 7 eV. The DFT result, confirmed by a more precise GW band calculation, is similar to that of a small gap non-Kondo nontopological semiconductor. Additionally, the pressure-dependent electronic structure of YbB_{6} is investigated theoretically and found to transform into a p-d overlap semimetal with small Yb mixed valency.
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Affiliation(s)
- Chang-Jong Kang
- Department of Physics, PCTP, Pohang University of Science and Technology, (POSTECH) Pohang 37673, Korea
| | - J D Denlinger
- Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720, USA
| | - J W Allen
- Department of Physics, Randall Laboratory, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Chul-Hee Min
- Universität Würzburg, Experimentelle Physik VII, 97074 Würzburg, Germany
| | - F Reinert
- Universität Würzburg, Experimentelle Physik VII, 97074 Würzburg, Germany
| | - B Y Kang
- School of Materials Science and Engineering, GIST, Gwangju 61005, Korea
| | - B K Cho
- School of Materials Science and Engineering, GIST, Gwangju 61005, Korea
| | - J-S Kang
- Department of Physics, The Catholic University of Korea, Bucheon 14662, Korea
| | - J H Shim
- Department of Physics, PCTP, Pohang University of Science and Technology, (POSTECH) Pohang 37673, Korea
- Department of Chemistry and Division of Advanced Nuclear Engineering, POSTECH, Pohang 37673, Korea
| | - B I Min
- Department of Physics, PCTP, Pohang University of Science and Technology, (POSTECH) Pohang 37673, Korea
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Wang B, Peng J, Xing DY, Wang J. Spin current due to spinlike Andreev reflection. PHYSICAL REVIEW LETTERS 2005; 95:086608. [PMID: 16196888 DOI: 10.1103/physrevlett.95.086608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2005] [Indexed: 05/04/2023]
Abstract
We propose theoretically a spinlike Andreev reflection that may occur at the interface of a semimetal and a doped excitonic insulator. In contrast to the usual Andreev reflection, this process does not produce the charge current, but gives rise to a pure spin current. Further investigation reveals the existence of a spinlike Josephson phenomenon between two excitonic insulators with ferromagnetism, which results in a dissipationless spin current. We stress that the present spin current satisfies the conservation condition and is quite different from the spin Hall current induced from spin-orbital interactions.
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Affiliation(s)
- Baigeng Wang
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
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Pereira VM, Lopes dos Santos JMB, Castro EV, Neto AHC. Double exchange model for magnetic hexaborides. PHYSICAL REVIEW LETTERS 2004; 93:147202. [PMID: 15524836 DOI: 10.1103/physrevlett.93.147202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2004] [Indexed: 05/24/2023]
Abstract
A microscopic theory for rare-earth ferromagnetic hexaborides, such as Eu1-xCaxB6, is proposed on the basis of the double-exchange Hamiltonian. In these systems, the reduced carrier concentrations place the Fermi level near the mobility edge, introduced in the spectral density by the disordered spin background. We show that the transport properties such as the Hall effect, magnetoresistance, frequency dependent conductivity, and dc resistivity can be quantitatively described within the model. We also make specific predictions for the behavior of the Curie temperature T(C) as a function of the plasma frequency omega(p).
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Affiliation(s)
- Vitor M Pereira
- Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA
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6
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Souma S, Komatsu H, Takahashi T, Kaji R, Sasaki T, Yokoo Y, Akimitsu J. Electronic band structure and Fermi surface of CaB6 studied by angle-resolved photoemission spectroscopy. PHYSICAL REVIEW LETTERS 2003; 90:027202. [PMID: 12570575 DOI: 10.1103/physrevlett.90.027202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2002] [Indexed: 05/24/2023]
Abstract
We report high-resolution angle-resolved photoemission spectroscopy (ARPES) on CaB6. The band structure determined by ARPES shows a 1 eV energy gap at the X point between the valence and the conduction bands. We found a small electron pocket at the X point, whose carrier number is estimated to be (4-5) x 10(19) cm(-3), in good agreement with the Hall resistivity measurement with the same crystal. The experimental results are discussed in comparison with band structure calculations and theoretical models for the high-temperature ferromagnetism.
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Affiliation(s)
- S Souma
- Department of Physics, Tohoku University, Sendai 980-8578, Japan
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Denlinger JD, Clack JA, Allen JW, Gweon GH, Poirier DM, Olson CG, Sarrao JL, Bianchi AD, Fisk Z. Bulk band gaps in divalent hexaborides. PHYSICAL REVIEW LETTERS 2002; 89:157601. [PMID: 12366022 DOI: 10.1103/physrevlett.89.157601] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2001] [Indexed: 05/23/2023]
Abstract
Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for many-body quasiparticle band calculations.
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Affiliation(s)
- J D Denlinger
- Advanced Light Source, Lawrence Berkeley National Laboratory, California 94720, USA
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Zong FH, Lin C, Ceperley DM. Spin polarization of the low-density three-dimensional electron gas. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 66:036703. [PMID: 12366294 DOI: 10.1103/physreve.66.036703] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2002] [Indexed: 05/23/2023]
Abstract
To determine the state of spin polarization of the three-dimensional electron gas at very low densities and zero temperature, we calculate the energy versus spin polarization using diffusion quantum Monte Carlo methods with backflow wave functions and twist averaged boundary conditions. We find a second-order phase transition to a partially polarized phase at r(s) approximately 50+/-2. The magnetic transition temperature is estimated using an effective mean-field method, the Stoner model.
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Affiliation(s)
- F H Zong
- Department of Physics and NCSA, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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Monnier R, Delley B. Point defects, ferromagnetism, and transport in calcium hexaboride. PHYSICAL REVIEW LETTERS 2001; 87:157204. [PMID: 11580724 DOI: 10.1103/physrevlett.87.157204] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2001] [Indexed: 05/23/2023]
Abstract
The formation energy and local magnetic moment of a series of point defects in CaB6 are computed using a supercell approach within the generalized gradient approximation to density functional theory. It is found that the substitution of Ca by La does not lead to the formation of a local moment, while a neutral B6 vacancy carries a moment of 2.4 Bohr magnetons. A plausible mechanism for the ferromagnetic ordering of these moments is suggested. Since the same broken B-B bonds appear on the preferred (100) cleavage planes of the CaB6 structure, it is argued that internal surfaces in polycrystals as well as external surfaces in general will make a large contribution to the observed magnetization.
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Affiliation(s)
- R Monnier
- Laboratorium für Festkörperphysik, ETH-Hönggerberg, CH-8093 Zürich, Switzerland
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Tromp HJ, van Gelderen P, Kelly PJ, Brocks G, Bobbert PA. CaB6: a new semiconducting material for spin electronics. PHYSICAL REVIEW LETTERS 2001; 87:016401. [PMID: 11461482 DOI: 10.1103/physrevlett.87.016401] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2000] [Indexed: 05/23/2023]
Abstract
Ferromagnetism was recently observed at unexpectedly high temperatures in La-doped CaB6. The starting point of all theoretical proposals to explain this observation is a semimetallic electronic structure calculated for CaB6 within the local density approximation. Here we report the results of parameter-free quasiparticle calculations of the single-particle excitation spectrum which show that CaB6 is not a semimetal but a semiconductor with a band gap of 0.8+/-0.1 eV. Magnetism in La(x)Ca1-xB6 occurs just on the metallic side of a Mott transition in the La-induced impurity band.
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Affiliation(s)
- H J Tromp
- Faculty of Applied Physics and MESA+ Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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