TopologyBased Method for Determining the Order Parameter of the Putative SpinTriplet Superconductor UTe_{2}
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Intrinsic Anomalous Thermal Hall Effect in the Unconventional Superconductor UTe_{2}
J. Phys. Soc. Jpn. 91, 094710 (2022).
The intrinsic anomalous thermal Hall effect can be an effective probe for the order parameters of nonunitary pairing states of the putative spintriplet superconductor UTe_{2}
Recently, the actinide compound UTe_{2} has been intensively studied as a novel candidate material for a spintriplet superconductor, which is expected to host Majorana particles utilized for quantum computation. The superconductivity of this material without a magnetic order renders it ideal for research on pure spintriplet superconductors. The possibility of a nonunitary pairing state in UTe_{2} is also discussed, indicating that UTe_{2} is a Weyl superconductor that has topologically protected point nodes with monopole charges in the superconducting gap. However, the symmetry and gap structures, which determine its topological properties, remain controversial. Therefore, an effective method for probing the order parameter of UTe_{2} is lacking.
In this study, the intrinsic anomalous thermal Hall effect, which is a fundamental property of Weyl superconductors, is investigated. The pairing state in the spintriplet superconductor is characterized by a threedimensional oddparity order parameter, referred to as a dvector. The basis of the dvector corresponds to the irreducible representations (IRs) of the D_{2h} point group. When symmetry is reduced by the application of an external field, the admixture of these IRs is formed, which results in nonunitary pairing. We calculate the thermal Hall conductivity for the possible nonunitary pairing states in UTe_{2} as a function of the ratio “r” of the amplitudes of two mixed IRs. The intrinsic anomalous thermal Hall conductivity can be obtained by the integration of the Chern number, which corresponds to an integration of the Berry curvature over the Brillouin zone. Since the Berry curvature arises from the Weyl point nodes with monopole charges, the intrinsic thermal Hall conductivity directly reflects the distribution of the point nodes on the Fermi surfaces.
The relationship between the Hall conductivity and the point node structure is evident in the case of a simple ellipsoidshaped Fermi surface, which is the minimum model that reflects the orthorhombic crystal structure. The admixture of IRs causes a splitting of the point nodes, because of which they move away from the highsymmetry axis. When one point node splits into two, the split nodes become Weyl points that have monopole charges with opposite signs. In this case, a Berry curvature exists along a certain direction, with a finite Chern number. This results in a finite thermal Hall conductivity, the magnitude of which depends on the distance between the point nodes.
The change in the point node structure due to the admixture of the two IRs is unique for each dvector and is useful for the distinction of the order parameters based on future thermal conductivity measurements.
(Written by Y. Moriya on behalf of all the authors.)
Intrinsic Anomalous Thermal Hall Effect in the Unconventional Superconductor UTe_{2}
J. Phys. Soc. Jpn. 91, 094710 (2022).
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