Tomoya Asaba

Rotational Symmetry Breaking in a Trigonal Superconductor Nb-doped Bi2Se3

The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi2Se3) is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb)-doped Bi2Se3. As a result, the in-plane magnetic torque signal vanishes every 60°. More importantly, the superconducting hysteresis loop amplitude is enhanced along one preferred direction, spontaneously breaking the rotational symmetry. This observation indicates the presence of nematic order in the superconducting ground state of Nb-doped Bi2Se3. DOI:https://doi.org/10.1103/PhysRevX.7.011009 Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Published by the American Physical Society

Magnetic phase diagram of underdoped YBa2Cu3Oy inferred from torque magnetization and thermal conductivity

Significance We obtain the magnetic phase diagram in the underdoped cuprate YBa2Cu3Oy using torque magnetometry at temperatures 0.3–70 K and magnetic fields up to 45 T. At low fields, vortices (quantized flux tubes) form a vortex solid that is strongly pinned to the lattice. At large fields, melting of the solid to a vortex liquid produces nonzero dissipation. However, the vortex liquid persists to fields above 41 T. We have also mapped out the “transition” fields at which the charge-density–wave state (observed in X-ray diffraction experiments) becomes stable. Our results show that, in intense fields, superconductivity adjusts to coexist with the charge-density wave, but the Cooper pairs, which define the superconducting fluid, survive to fields well above 41 T. Strong evidence for charge-density correlation in the underdoped phase of the cuprate YBa2Cu3Oy was obtained by NMR and resonant X-ray scattering. The fluctuations were found to be enhanced in strong magnetic fields. Recently, 3D charge-density–wave (CDW) formation with long-range order (LRO) was observed by X-ray diffraction in H> 15 T. To elucidate how the CDW transition impacts the pair condensate, we have used torque magnetization to 45 T and thermal conductivity κxx to construct the magnetic phase diagram in untwinned crystals with hole density p = 0.11. We show that the 3D CDW transitions appear as sharp features in the susceptibility and κxx at the fields HK and Hp, which define phase boundaries in agreement with spectroscopic techniques. From measurements of the melting field Hm(T) of the vortex solid, we obtain evidence for two vortex solid states below 8 K. At 0.5 K, the pair condensate appears to adjust to the 3D CDW by a sharp transition at 24 T between two vortex solids with very different shear moduli. At even higher H (41 T), the second vortex solid melts to a vortex liquid which survives to fields well above 41 T. de Haas–van Alphen oscillations appear at fields 24–28 T, below the lower bound for the upper critical field Hc2.

Quantum oscillations in CuxBi2Se3 in high magnetic fields

Cu

Magnetotransport measurements of the surface states of samarium hexaboride using Corbino structures

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Bulk Rotational Symmetry Breaking in Kondo Insulator SmB6

Bi

Magnetic Field Enhanced Superconductivity in Epitaxial Thin Film WTe 2

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Quantum oscillations of electrical resistivity in an insulator

Se

Quantum Oscillations in Cu x Bi 2 Se 3 in High Magnetic Fields

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Enhancement of thermal conductivity across the metal-insulator transition in vanadium dioxide

has drawn much attention as the leading candidate to be the first topological superconductor and the realization of coveted Majorana particles in a condensed matter system. However, there has been increasing controversy about the nature of its superconducting phase. This study sheds light on present ambiguity in the normal state electronic state, by providing a complete look at the quantum oscillations in magnetization in Cu

Probing the thermal Hall effect using miniature capacitive strontium titanate thermometry

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