Origin of Metamagnetic Transition (MMT) in the Spin-Triplet Superconductivity in UTe2
© The Physical Society of Japan
This article is on
Magnetovolume Effect on the First-Order Metamagnetic Transition in UTe2
(JPSJ Editors' Choice)
J. Phys. Soc. Jpn. 91, 063703 (2022).
State-of-the-art magnetostriction measurements in a pulsed-magnetic field reveal the origin of a metamagnetic transition of spin-triplet superconductor UTe2. We propose that the uranium valence fluctuation plays a crucial role in its metamagnetic and superconducting transitions.

The metamagnetism realized in heavy fermion systems has been well studied to date. At the metamagnetic transition/crossover fields, magnetization increases discontinuously/non-lineally, and fluctuations develop. Consequently, the effective mass increases. Thus, the metamagnetism may induce a new quantum state, such as a superconducting transition. The uranium-based ferromagnetic superconductors have been good playgrounds to study the relationship between metamagnetism and superconductivity. Quite recently, another related system, UTe2, was discovered.
The superconductivity in a paramagnetic heavy fermion system, UTe2, became a hot topic in condensed matter physics community since the realization of the spin-triplet state, which is expected for use in quantum computing. The external stimuli, such as pressure, magnetic field, and its applied direction, make UTe2 more attractive. The most remarkable feature is the magnetic-field-direction controlled superconductivity. For H || b axis, superconductivity is reinforced by increasing the fields but is killed at the metamagnetic field Hm ~ 35 T, where a first-order metamagnetic transition takes place. However, the field applied near the orthorhombic [011] direction induces another superconducting phase above Hm. Because experimental probes usable under such extreme conditions were limited, the role of metamagnetic transition in the appearance/disappearance of superconductivity is far from complete understanding. Moreover, the metamagnetism in UTe2 must be more clarified. These still remain a big challenge for experimentalists.
Magnetostriction, that is, the length/volume change with magnetic field, should offer hints at the aforementioned issues. The authors have developed magnetostriction measurements combining the fiber Bragg grating fiber optics and optical filter method that cover a wide range of ultra-high-magnetic fields beyond 100 T. A new attempt demonstrated in this article is simultaneous magnetostriction measurements up to 55 T. We obtained the linear magnetostriction along the two principal axes within a one-field scan; thus, we could perform measurements efficiently. This improvement also enables us to confirm the reliability and reproducibility of the magnetostriction measurements. Using a single crystal of UTe2, we revealed the magnetostrictions along all principal axes and the volume change at Hm.
Across Hm approaching from the lower fields, the volume shrinks discontinuously. This volume discontinuity well explains the pressure dependence of Hm and magnetic susceptibility reported earlier. Furthermore, we revealed that the metamagnetic transition in UTe2 involves anisotropic lattice deformation. Considering the localized and itinerant duality nature of uranium ions, we proposed that the uranium valence transition is the origin of metamagnetism. We also discussed the singular behavior in UTe2
by comparing it with the other heavy fermion systems. Our findings deepen the understanding of the fascinated physics realized in UTe2.
(The figure has been replaced as of July 19, 2022)
(Written by A. Miyake on behalf of all authors)
Magnetovolume Effect on the First-Order Metamagnetic Transition in UTe2
(JPSJ Editors' Choice)
J. Phys. Soc. Jpn. 91, 063703 (2022).
Share this topic
Fields
Related Articles
-
Thickness-Dependent Oscillation Behavior of Magnetic Phase Transitions in Pt Ultrathin Films with Small Orbital Moment
Magnetic properties in condensed matter
2023-1-6
Ferromagnetism in nano-Pt films originates from the quantum-confinement effect that depends on film thickness. Studies of the electronic states of nano-Pt will aid in developing methods for efficiently utilizing its large spin-orbit coupling.
-
High Magnetic Field as a Tool for Discovery in Condensed Matter Physics
Magnetic properties in condensed matter
Dielectric, optical, and other properties in condensed matter
Electronic transport in condensed matter
Structure and mechanical and thermal properties in condensed matter
Electron states in condensed matter
Electronic structure and electrical properties of surfaces and nanostructures
Measurement, instrumentation, and techniques
2022-12-13
The Journal of the Physical Society of Japan highlights in this special topic recent advances in modern physics that have been realized with the generation of pulsed high magnetic fields.
-
Understanding the Obscure Antiferromagnetism in α-Mn by Nuclear Magnetic Resonance
Magnetic properties in condensed matter
2022-11-29
Although Mn is an elementary metal, the antiferromagnetic state of α-Mn is still obscure. Our NMR study on high-quality α-Mn provides new insights into the symmetry of its antiferromagnetism.
-
Observing the de Haas–van Alphen Effect to Unveil the Electronic Structure of UTe2 Superconductor
Electron states in condensed matter
Superconductivity
2022-11-16
The topology of Fermi surfaces with heavy effective masses in strongly correlated topological superconductor UTe2 was investigated using quantum oscillation measurements and theoretical calculations.
-
Strange Metal Behavior Potentially Associated to Hidden Electronic Nematicity
Superconductivity
Electronic transport in condensed matter
2022-11-10
Iron-based superconductor, Ba1-xRbxFe2As2, exhibits “strange metal” behavior—linear dependence of resistivity on temperature. It seems that hidden electronic nematic fluctuations play a greater role than the well-known antiferromagnetic fluctuations.