C. Meingast
Karlsruhe Institute of Technology
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Featured researches published by C. Meingast.
Physical Review B | 2015
Watson; T. K. Kim; Amir A. Haghighirad; Nr Davies; Alix McCollam; A. Narayanan; S.F. Blake; Yulin Chen; S. Ghannadzadeh; Aj Schofield; M. Hoesch; C. Meingast; Th. Wolf; Amalia I. Coldea
We present a comprehensive study of the evolution of the nematic electronic structure of FeSe using high-resolution angle-resolved photoemission spectroscopy (ARPES), quantum oscillations in the normal state, and elastoresistance measurements. Our high-resolution ARPES allows us to track the Fermi surface deformation from fourfold to twofold symmetry across the structural transition at ∼87K, which is stabilized as a result of the dramatic splitting of bands associated with dxz and dyz character in the presence of strong electronic interactions. The low-temperature Fermi surface is that of a compensated metal consisting of one hole and two electron bands and is fully determined by combining the knowledge from ARPES and quantum oscillations. A manifestation of the nematic state is the significant increase in the nematic susceptibility approaching the structural transition that we detect from our elastoresistance measurements on FeSe. The dramatic changes in electronic structure cannot be explained by the small lattice distortion and, in the absence of magnetic fluctuations above the structural transition, point clearly towards an electronically driven transition in FeSe, stabilized by orbital-charge ordering.
Physical Review B | 2013
A. E. Böhmer; F. Hardy; F. Eilers; D. Ernst; P. Adelmann; P. Schweiss; Th. Wolf; C. Meingast
The coupling between superconductivity and orthorhombic distortion is studied in vapor-grown FeSe single crystals using high-resolution thermal-expansion measurements. In contrast to the Ba122-based (Ba122) superconductors, we find that superconductivity does not reduce the orthorhombicity below
Physical Review B | 2014
Taichi Terashima; Naoki Kikugawa; Andhika Kiswandhi; Eun Sang Choi; J. S. Brooks; S. Kasahara; Tatsuya Watashige; Hiroaki Ikeda; T. Shibauchi; Y. Matsuda; Thomas Wolf; A. E. Böhmer; F. Hardy; C. Meingast; H. v. Löhneysen; Michi-To Suzuki; Ryotaro Arita; Shinya Uji
{T}_{c}
Physical Review Letters | 2014
A. E. Böhmer; Philipp Burger; F. Hardy; Th. Wolf; P. Schweiss; Rainer Fromknecht; Marius Reinecker; W. Schranz; C. Meingast
. Instead we find that superconductivity couples strongly to the in-plane area, which explains the large hydrostatic pressure effects. We discuss our results in light of the spin-nematic scenario and argue that FeSe has many features that are quite different from typical Fe-based superconductors.
Physical Review Letters | 2013
F. Hardy; A. E. Böhmer; Dai Aoki; Philipp Burger; Th. Wolf; P. Schweiss; Rolf Heid; P. Adelmann; Y. X. Yao; G. Kotliar; Jörg Schmalian; C. Meingast
We have observed Shubnikov-de Haas oscillations in FeSe. The Fermi surface deviates significantly from predictions of band-structure calculations and most likely consists of one electron and one hole thin cylinder. The carrier density is in the order of 0.01 carriers/ Fe, an order-of-magnitude smaller than predicted. Effective Fermi energies as small as 3.6 meV are estimated. These findings call for elaborate theoretical investigations incorporating both electronic correlations and orbital ordering.
Physica C-superconductivity and Its Applications | 1993
O. Kraut; C. Meingast; G. Bräuchle; Helmut Claus; A. Erb; G. Müller-Vogt; H. Wühl
The nematic susceptibility, χφ, of hole-doped Ba(1-x)K(x)Fe2As2 and electron-doped Ba(Fe(1-x)Co(x))2As2 iron-based superconductors is obtained from measurements of the elastic shear modulus using a three-point bending setup in a capacitance dilatometer. Nematic fluctuations, although weakened by doping, extend over the whole superconducting dome in both systems, suggesting their close tie to superconductivity. Evidence for quantum critical behavior of χφ is, surprisingly, only found for Ba(Fe(1-x)Co(x))2As2 and not for Ba(1-x)K(x)Fe2As2--the system with the higher maximal Tc value.
Physical Review Letters | 2001
C. Meingast; Volker Pasler; P. Nagel; A. I. Rykov; S. Tajima; Peter Olsson
Using resistivity, heat-capacity, thermal-expansion, and susceptibility measurements we study the normal-state behavior of KFe2As2. Both the Sommerfeld coefficient (γ≈103 mJ mol(-1) K(-2)) and the Pauli susceptibility (χ≈4×10(-4)) are strongly enhanced, which confirm the existence of heavy quasiparticles inferred from previous de Haas-van Alphen and angle-resolved photoemission spectroscopy experiments. We discuss this large enhancement using a Gutzwiller slave-boson mean-field calculation, which shows the proximity of KFe2As2 to an orbital-selective Mott transition. The temperature dependence of the magnetic susceptibility and the thermal expansion provide strong experimental evidence for the existence of a coherence-incoherence crossover, similar to what is found in heavy fermion and ruthenate compounds, due to Hunds coupling between orbitals.
Physical Review B | 2010
F. Hardy; Th. Wolf; R. A. Fisher; Robert Eder; P. Schweiss; P. Adelmann; H. v. Löhneysen; C. Meingast
Abstract The dependence of Tc on uniaxial pressure dTc/dpi(i= a, b, c) is determined for untwinned YBa2Cu3Ox single crystals as a function of O-content using ultrahigh-resolution thermal-expansion data and the Ehrenfest relationship. The dTc/dpi values are found to be highly anisotropic and are likely due to several different effects. For uniaxial-pressure applied parallel to the c-axis, we find a strong O-content (or carrier density) dependence of the dTc/dpb values, which have opposite signs charge transfer model. This model does not, however, explain the large dTc/dpa and dTc/dpb values, which have opposite signs and do not show a strong O-content dependence except at x=6.7, where both dTc/dpa and dTc/dpb values increase sharply. The a, b effects are discussed in terms of the orthorhombic distortion.
Physical Review Letters | 1998
Volker Pasler; P. Schweiss; C. Meingast; Bernhard Obst; H. Wühl; Alexandre I. Rykov; S. Tajima
: The thermodynamics of the superconducting transition is studied as a function of doping using high-resolution expansivity data of YBa(2)Cu(3)O (x) single crystals and Monte Carlo simulations of the anisotropic 3D- XY model. We directly show that T(c) of underdoped YBa(2)Cu(3)O (x) is strongly suppressed from its mean-field value (T(MF)(c)) by phase fluctuations of the superconducting order parameter. For overdoped YBa(2)Cu(3)O (x) fluctuation effects are greatly reduced and T(c) approximately T(MF)(c). We find that T(MF)(c) exhibits a similar doping dependence as the pseudogap energy, naturally suggesting that the pseudogap arises from phase-incoherent Cooper pairing.
Physical Review Letters | 2013
Rafael M. Fernandes; A. E. Böhmer; C. Meingast; Jörg Schmalian
We report on the determination of the electronic heat capacity of a slightly overdoped (x = 0.075) Ba(Fe1-xCox)2As2 single crystal with a Tc of 21.4 K. Our analysis of the temperature dependence of the superconducting-state specific heat provides strong evidence for a two-band s-wave order parameter with gap amplitudes 2D1(0)/kBTc=1.9 and 2D2(0)/kBTc=4.4. Our result is consistent with the recently predicted s+- order parameter [I. I. Mazin et al., Phys. Rev. Lett. 101, 057003 (2008)].