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Intimate relationship between spin configuration in the triplet pair and superconductivity in UTe$_2$
Authors:
Hiroki Matsumura,
Yuki Takahashi,
Riku Matsubayashi,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Motoi Kimata,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Atsushi Miyake,
Dai Aoki,
Tetsuya Furukawa,
Takahiro Sasaki
Abstract:
Spin-triplet superconductivity is an intriguing quantum coherent state with both spin and orbital degrees of freedom, which holds significant potential for future applications in quantum technology. However, how the spin of the triplet pairs responds to an external magnetic field remains poorly understood. This is mainly due to the absence of suitable spin-triplet superconductors. Here, we report…
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Spin-triplet superconductivity is an intriguing quantum coherent state with both spin and orbital degrees of freedom, which holds significant potential for future applications in quantum technology. However, how the spin of the triplet pairs responds to an external magnetic field remains poorly understood. This is mainly due to the absence of suitable spin-triplet superconductors. Here, we report results of Knight-shift and ac-susceptibility measurements on UTe$_2$. We demonstrate that the spin susceptibility, which slightly decreases compared to the normal-state value below the superconducting (SC) transition temperature $T_{\rm c}$, is rapidly restored and nearly recovers to the normal-state values around 5 T, well below the SC upper critical field $H_{c2}$ when the magnetic field is applied along the $c$ axis ($H \parallel c$). In addition, we found that $H_{\rm c2}$ of superconductivity becomes larger when the SC spin aligns with the magnetic field. By considering the results on $H \parallel b$, our results suggest the presence of a close relationship between the spin configuration of the triplet pair and $H_{\rm c2}$, as well as the anisotropic pinning interaction acting on the triplet pairs. These phenomena, which have never been observed in spin-singlet superconductors, represent characteristic features unique to spin-triplet superconductors. We discuss the similarities between superconductivity in UTe$_2$ and superfluid $^3$He, focusing on their spin-triplet pairing states.
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Submitted 9 February, 2026;
originally announced February 2026.
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$b$-axis and $c$-axis Knight shift measurements in the superconducting state on ultraclean UTe$_2$ with $T_c$ = 2.1 K
Authors:
Hiroki Matsumura,
Yuki Takahashi,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Atsushi Miyake,
Dai Aoki
Abstract:
Knight shifts along the $b$ and $c$ axes ($K_b$ and $K_c$) at two crystallographically distinct Te sites were measured down to 70 mK using $^{125}$Te nuclear magnetic resonance (NMR) on an ultraclean UTe$_2$ single crystal with a superconducting (SC) transition temperature $T_{\mathrm{c}}$ = 2.1 K. This was carried out to determine the $\boldsymbol{d}$-vector components, which are the order parame…
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Knight shifts along the $b$ and $c$ axes ($K_b$ and $K_c$) at two crystallographically distinct Te sites were measured down to 70 mK using $^{125}$Te nuclear magnetic resonance (NMR) on an ultraclean UTe$_2$ single crystal with a superconducting (SC) transition temperature $T_{\mathrm{c}}$ = 2.1 K. This was carried out to determine the $\boldsymbol{d}$-vector components, which are the order parameter in the spin-triplet pairing. Although the decrease in $K_b$ and $K_c$ is comparable to the theoretical estimation of the SC diamagnetic shielding effect, it is confirmed, by taking the difference between two Knight shifts at the distinct Te sites, that the spin susceptibility along the $b$ and $c$ axes decreases in the SC state. Taking into account the large decrease in $K_a$ in the SC state, we conclude that the $\boldsymbol{d}$ vector has components along all three crystal axes.
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Submitted 26 May, 2025;
originally announced May 2025.
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Born-limit scattering and pair-breaking crossover in d-wave superconductivity of (TMTSF)2ClO4
Authors:
Shota Yano,
Kazumi Fukushima,
Katsuki Kinjo,
Soichiro Yamane,
Le Hong Hoàng To,
Pascale Senzier,
Cécile Mézière,
Shamashis Sengupta,
Claire A Marrache-Kikuchi,
Denis Jerome,
Shingo Yonezawa
Abstract:
In the quasi-one-dimensional organic unconventional superconductor (TMTSF)2ClO4, the randomness of the non-centrosymmetric ClO4 anions can be experimentally controlled by adjusting the cooling rate through the anion-ordering temperature. This feature provides a unique opportunity to study disorder effects on unconventional superconductivity in great detail. We here report on measurements of the el…
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In the quasi-one-dimensional organic unconventional superconductor (TMTSF)2ClO4, the randomness of the non-centrosymmetric ClO4 anions can be experimentally controlled by adjusting the cooling rate through the anion-ordering temperature. This feature provides a unique opportunity to study disorder effects on unconventional superconductivity in great detail. We here report on measurements of the electronic specific heat of this system, performed under various cooling rates. The evolution of the residual density of states indicates that the ClO4 randomness works as Born-limit pair breakers, which, to our knowledge, has never been clearly identified in any unconventional superconductors. Furthermore, detailed analyses suggest a peculiar crossover from strong unitarity scattering due to molecular defects toward the Born-limit weak scattering due to borders of ordered regions. This work supports the d-wave nature of pairing in (TMTSF)2ClO4 and intends to provide an experimental basis for further developments of pair-breaking theories of unconventional superconductors where multiple electron scattering mechanisms coexist.
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Submitted 16 May, 2025;
originally announced May 2025.
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Intrinsic low-temperature magnetic properties on the ultra-clean UTe$_2$ with $T_{\rm c}$ = 2.1 K revealed by $^{125}$Te NMR
Authors:
Hiroki Matsumura,
Shunsaku Kitagawa,
Shiki Ogata,
Riku Matsubayashi,
Hiroki Fujibayashi,
Katsuki Kinjo,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Atsushi Miyake,
Dai Aoki
Abstract:
To investigate the intrinsic magnetic properties of UTe$_2$, we performed $^{125}$Te-NMR measurements on the ultra-clean single-crystalline UTe$_2$ with superconducting transition temperature $T_{\rm c}$ = 2.1~K and compared the results with those of the $T_{\rm c}$ = 1.6~K sample. The broadening of the linewidth of the NMR spectrum in the $a$-axis magnetic field and the low-temperature magnetic f…
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To investigate the intrinsic magnetic properties of UTe$_2$, we performed $^{125}$Te-NMR measurements on the ultra-clean single-crystalline UTe$_2$ with superconducting transition temperature $T_{\rm c}$ = 2.1~K and compared the results with those of the $T_{\rm c}$ = 1.6~K sample. The broadening of the linewidth of the NMR spectrum in the $a$-axis magnetic field and the low-temperature magnetic fluctuations observed in the 1.6~K sample are suppressed in the ultra-clean sample, indicating that such magnetic properties originate from a tiny amount of U deficiency. The present results suggest that the magnetic properties in UTe$_2$ are sensitive to the U deficiency. We also observed a peculiar angular dependence of the NMR quantities due to large magnetic anisotropy with the $a$-axis as the magnetic easy axis.
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Submitted 13 March, 2025; v1 submitted 12 March, 2025;
originally announced March 2025.
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Appearance of $c$-axis magnetic moment in odd-parity antiferromagnetic state in CeRh$_2$As$_2$ revealed by $^{75}$As-NMR
Authors:
Shiki Ogata,
Shunsaku Kitagawa,
Katsuki Kinjo,
Kenji Ishida,
Manuel Brando,
Elena Hassinger,
Christoph Geibel,
Seunghyun Khim
Abstract:
CeRh$_2$As$_2$ shows the superconducting (SC) multiphase under the $c$-axis magnetic field, which is considered to originate from local inversion symmetry breaking at the Ce site. We reported that the antiferromagnetic (AFM) order is inside the SC phase and that the AFM state disappears at the transition field to the high-field SC phase. However, the magnetic structure in the AFM state has not bee…
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CeRh$_2$As$_2$ shows the superconducting (SC) multiphase under the $c$-axis magnetic field, which is considered to originate from local inversion symmetry breaking at the Ce site. We reported that the antiferromagnetic (AFM) order is inside the SC phase and that the AFM state disappears at the transition field to the high-field SC phase. However, the magnetic structure in the AFM state has not been clarified yet. In this study, we performed $^{75}$As-NMR measurements in the SC phase in $H\parallel [110]$ to identify the magnetic structure. Comparing the NMR linewidth with $H \parallel c$, we found that the internal magnetic field is oriented to the $c$ axis. This suggests a $q = 0$ $A$-type AFM with the moments parallel to the $c$ axis. We also observed the reduction of the spin susceptibility, which indicates spin-singlet superconductivity in the low-field SC phase. This study provides an important clue to clarify the correlation between the SC multiphase, magnetism, and local inversion symmetry breaking.
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Submitted 13 December, 2024;
originally announced December 2024.
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Investigation of the hyperfine coupling constant of locally noncentrosymmetric heavy-fermion superconductor CeRh$_{2}$As$_{2}$
Authors:
Shiki Ogata,
Shunsaku Kitagawa,
Katsuki Kinjo,
Mayu Kibune,
Kenji Ishida,
Manuel Brando,
Elena Hassinger,
Christoph Geibel,
Seunghyun Khim
Abstract:
We performed $^{75}$As-NMR measurements in $H\parallel ab$ to investigate the normal-state magnetic properties of CeRh$_2$As$_2$, a recently-discovered heavy-fermion superconductor. We compared the NMR Knight shift $K$ with the magnetic susceptibility $χ_{ab}$, and estimated the hyperfine coupling constant $A_{\mathrm{hf}}$ from the slope of the $K-χ$ plot. We observed that the magnitude of…
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We performed $^{75}$As-NMR measurements in $H\parallel ab$ to investigate the normal-state magnetic properties of CeRh$_2$As$_2$, a recently-discovered heavy-fermion superconductor. We compared the NMR Knight shift $K$ with the magnetic susceptibility $χ_{ab}$, and estimated the hyperfine coupling constant $A_{\mathrm{hf}}$ from the slope of the $K-χ$ plot. We observed that the magnitude of $A_{\mathrm{hf},ab}$ at the As(1) site changes at around 20 K owing to emerging the heavy-fermion state, which was also observed in $A_{\mathrm{hf}}$ at the As(2) site and in $H\parallel c$. The sign of $A_{\mathrm{hf},ab}$ at the As(1) site is negative in low temperature. These are important for the analysis of the NMR results of CeRh$_2$As$_2$ in the superconducting state.
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Submitted 24 January, 2024;
originally announced January 2024.
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Unveiling exotic magnetic phase diagram of a non-Heisenberg quasicrystal approximant
Authors:
Farid Labib,
Kazuhiro Nawa,
Shintaro Suzuki,
Hung-Cheng Wu,
Asuka Ishikawa,
Kazuki Inagaki,
Takenori Fujii,
Katsuki Kinjo,
Taku J. Sato,
Ryuji Tamura
Abstract:
A magnetic phase diagram of the non-Heisenberg Tsai-type 1/1 Au-Ga-Tb approximant crystal (AC) has been established across a wide electron-per-atom (e/a) range via magnetization and powder neutron diffraction measurements. The diagram revealed exotic ferromagnetic (FM) and antiferromagnetic (AFM) orders that originate from the unique local spin icosahedron common to icosahedral quasicrystals (iQCs…
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A magnetic phase diagram of the non-Heisenberg Tsai-type 1/1 Au-Ga-Tb approximant crystal (AC) has been established across a wide electron-per-atom (e/a) range via magnetization and powder neutron diffraction measurements. The diagram revealed exotic ferromagnetic (FM) and antiferromagnetic (AFM) orders that originate from the unique local spin icosahedron common to icosahedral quasicrystals (iQCs) and ACs; The noncoplanar whirling AFM order is stabilized as the ground state at the e/a of 1.72 or less whereas a noncoplanar whirling FM order was found at the larger e/a of 1.80, with magnetic moments tangential to the Tb icosahedron in both cases. Moreover, the FM/AFM phase selection rule was unveiled in terms of the nearest neighbour (J1) and next nearest neighbour (J2) interactions by numerical calculations on a non-Heisenberg single icosahedron. The present findings will pave the way for understanding the intriguing magnetic orders of not only non-Heisenberg FM/AFM ACs but also non-Heisenberg FM/AFM iQCs, the latter of which are yet to be discovered.
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Submitted 22 October, 2023;
originally announced October 2023.
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Comparison of gap-based and flow-based control strategies using a new controlled stochastic cellular automaton model for traffic flow
Authors:
Kayo Kinjo,
Akiyasu Tomoeda
Abstract:
Autonomous vehicles are essential to future transportation systems, potentially reducing traffic congestion. This study examines the impact of different vehicle control strategies on traffic flow through simulations. We propose a novel stochastic cellular automaton model, the controlled stochastic optimal velocity (CSOV) model, which incorporates vehicle control effects. Within the CSOV model, two…
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Autonomous vehicles are essential to future transportation systems, potentially reducing traffic congestion. This study examines the impact of different vehicle control strategies on traffic flow through simulations. We propose a novel stochastic cellular automaton model, the controlled stochastic optimal velocity (CSOV) model, which incorporates vehicle control effects. Within the CSOV model, two control strategies are implemented: gap-based control (GC), which adjusts vehicle velocity to balance the gaps between adjacent vehicles, and flow-based control (FC), which aims to maintain a consistent local flow between the front and rear vehicles. Results show that both control strategies improve traffic flow. However, under weaker control, the GC sometimes resulted in lower flow compared to no control. In contrast, the FC consistently enhanced flow across control strengths, yielding more robust outcomes. Furthermore, when both strategies achieved comparable flow rates, the FC provided a more stable velocity distribution under varying traffic densities than the GC.
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Submitted 13 November, 2024; v1 submitted 28 August, 2023;
originally announced August 2023.
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Superconducting-Spin Reorientation in Spin-Triplet Multiple Superconducting Phases of UTe2
Authors:
Katsuki Kinjo,
Hiroki Fujibayashi,
Hiroki Matsumura,
Fumiya Hori,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Dai Aoki
Abstract:
Superconducting (SC) state has spin and orbital degrees of freedom, and spin-triplet superconductivity shows multiple SC phases due to the presence of these degrees of freedom. However, the observation of spin-direction rotation occurring inside the SC state (SC spin rotation) has hardly been reported. UTe2, a recently discovered topological superconductor, exhibits various SC phases under pressur…
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Superconducting (SC) state has spin and orbital degrees of freedom, and spin-triplet superconductivity shows multiple SC phases due to the presence of these degrees of freedom. However, the observation of spin-direction rotation occurring inside the SC state (SC spin rotation) has hardly been reported. UTe2, a recently discovered topological superconductor, exhibits various SC phases under pressure: SC state at ambient pressure (SC1), high-temperature SC state above 0.5 GPa (SC2), and low-temperature SC state above 0.5 GPa (SC3). We performed nuclear magnetic resonance and AC susceptibility measurements on single-crystal UTe2. The b-axis spin susceptibility remains unchanged in SC2, unlike in SC1, and decreases below the SC2-SC3 transition with spin modulation. These unique properties in SC3 arise from the coexistence of two SC order parameters. Our NMR results confirm the spin-triplet superconductivity with SC spin parallel to b in SC2, and unveil the remaining of spin degrees of freedom in superconducting UTe2.
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Submitted 28 July, 2023;
originally announced July 2023.
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Low-temperature Magnetic Fluctuations Investigated by $^{125}$Te-NMR on the Uranium-based Superconductor UTe$_{2}$
Authors:
Hiroki Fujibayashi,
Katsuki Kinjo,
Genki Nakamine,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Dai Aoki
Abstract:
To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe$_{2}$, we measured the NMR Knight shift $K$ and the nuclear spin-lattice relaxation rate $1/T_{1}$ in $H \parallel a$ by $^{125}$Te-NMR on a $^{125}$Te-enriched single-crystal sample. $1/T_1T$ in $H \parallel a$ is much smaller than $1/T_1T$ in $H \parallel b$ and $c$, and magnetic fluctuations along…
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To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe$_{2}$, we measured the NMR Knight shift $K$ and the nuclear spin-lattice relaxation rate $1/T_{1}$ in $H \parallel a$ by $^{125}$Te-NMR on a $^{125}$Te-enriched single-crystal sample. $1/T_1T$ in $H \parallel a$ is much smaller than $1/T_1T$ in $H \parallel b$ and $c$, and magnetic fluctuations along each axis are derived from the $1/T_1T$ measured in $H$ parallel to all three crystalline axes. The magnetic fluctuations are almost identical at two Te sites and isotropic at high temperatures, but become anisotropic below 40 K, where heavy-fermion state is formed. The character of magnetic fluctuations in UTe$_2$ is discussed with the comparison to its static susceptibility and the results on other U-based superconductors. It is considered that the magnetic fluctuations probed with the NMR measurements are determined by the magnetic properties inside the two-leg ladder formed by U atoms, which are dominated by the $q_a$ = 0 ferromagnetic fluctuations.
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Submitted 2 May, 2023;
originally announced May 2023.
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Large Reduction in the $a$-axis Knight Shift on UTe$_2$ with $T_{\rm c}$ = 2.1 K
Authors:
Hiroki Matsumura,
Hiroki Fujibayashi,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Dai Aoki
Abstract:
Spin susceptibility in the superconducting (SC) state was measured in the higher-quality sample of uranium-based superconductor UTe$_2$ by using Knight-shift measurements for a magnetic field $H$ along all three crystalline axes. In the higher-quality sample, the SC transition temperature $T_{\rm c}$ is about 2.1 K, and the residual electronic term in the specific heat is almost zero. The NMR line…
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Spin susceptibility in the superconducting (SC) state was measured in the higher-quality sample of uranium-based superconductor UTe$_2$ by using Knight-shift measurements for a magnetic field $H$ along all three crystalline axes. In the higher-quality sample, the SC transition temperature $T_{\rm c}$ is about 2.1 K, and the residual electronic term in the specific heat is almost zero. The NMR linewidth becomes narrower and is almost half of that in the previous sample with $T_{\rm c} \sim 1.6$ K when $H \parallel a$ and $c$. Although the Knight-shift behavior was not so different from the previous results for $H \parallel b$, and $c$, a large reduction in Knight shift along the $a$ axis was observed, in contrast with the previous $a$-axis Knight shift result. We discuss the origin of the difference between the previous and present results, and the possible SC state derived from the present results.
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Submitted 2 May, 2023;
originally announced May 2023.
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Parity transition of spin-singlet superconductivity using sub-lattice degrees of freedom
Authors:
Shiki Ogata,
Shunsaku Kitagawa,
Katsuki Kinjo,
Kenji Ishida,
Manuel Brando,
Elena Hassinger,
Christoph Geibel,
Seunghyun Khim
Abstract:
Recently, a superconducting (SC) transition from low-field (LF) to high-field (HF) SC states was reported in CeRh$_2$As$_2$, indicating the existence of multiple SC states. It has been theoretically noted that the existence of two Ce sites in the unit cell, the so-called sub-lattice degrees of freedom owing to the local inversion symmetry breaking at the Ce sites, can lead to the appearance of mul…
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Recently, a superconducting (SC) transition from low-field (LF) to high-field (HF) SC states was reported in CeRh$_2$As$_2$, indicating the existence of multiple SC states. It has been theoretically noted that the existence of two Ce sites in the unit cell, the so-called sub-lattice degrees of freedom owing to the local inversion symmetry breaking at the Ce sites, can lead to the appearance of multiple SC phases even under an interaction inducing spin-singlet superconductivity. CeRh$_2$As$_2$ is considered as the first example of multiple SC phases owing to this sub-lattice degree of freedom. However, microscopic information about the SC states has not yet been reported. In this study, we measured the SC spin susceptibility at two crystallographically inequivalent As sites using nuclear magnetic resonance for various magnetic fields. Our experimental results strongly indicate a spin-singlet state in both SC phases. In addition, the antiferromagnetic phase, which appears within the SC phase, only coexists with the LF SC phase; there is no sign of magnetic ordering in the HF SC phase. The present work reveals unique SC properties originating from the locally noncentrosymmetric characteristics.
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Submitted 19 April, 2023;
originally announced April 2023.
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Site Split of Antiferromagnetic $α$-Mn Revealed by $^{55}$Mn Nuclear Magnetic Resonance
Authors:
Masahiro Manago,
Gaku Motoyama,
Shijo Nishigori,
Kenji Fujiwara,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Kazuto Akiba,
Shingo Araki,
Tatsuo C. Kobayashi,
Hisatomo Harima
Abstract:
The magnetic structure of antiferromagnetic $α$-Mn has been unclarified for almost 70 years since its magnetism was discovered. We measured the zero-field nuclear magnetic resonance spectra of antiferromagnetic $α$-Mn to obtain further insight into magnetism below $T_{\text{N}} = 95$ K. The site II spectra split into two sites with five subpeaks owing to quadrupole interaction, and this shows that…
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The magnetic structure of antiferromagnetic $α$-Mn has been unclarified for almost 70 years since its magnetism was discovered. We measured the zero-field nuclear magnetic resonance spectra of antiferromagnetic $α$-Mn to obtain further insight into magnetism below $T_{\text{N}} = 95$ K. The site II spectra split into two sites with five subpeaks owing to quadrupole interaction, and this shows that the ordered moments at site II are slightly tilted from the $[001]$ direction. The site III spectra revealed that this site splits into four sites below $T_{\text{N}}$. These findings clearly demonstrate that the antiferromagnetic $α$-Mn symmetry is lower than previously considered.
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Submitted 6 October, 2022;
originally announced October 2022.
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Dynamics of quantum double dark-solitons and an exact finite-size scaling of Bose-Einstein condensation
Authors:
Kayo Kinjo,
Jun Sato,
Tetsuo Deguchi
Abstract:
We show several novel aspects in the exact non-equilibrium dynamics of quantum double dark-soliton states in the Lieb-Liniger model for the one-dimensional Bose gas with repulsive interactions. We also show an exact finite-size scaling of the fraction of the Bose-Einstein condensation (BEC) in the ground state, which should characterize the quasi-BEC in quantum double dark-soliton states that we a…
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We show several novel aspects in the exact non-equilibrium dynamics of quantum double dark-soliton states in the Lieb-Liniger model for the one-dimensional Bose gas with repulsive interactions. We also show an exact finite-size scaling of the fraction of the Bose-Einstein condensation (BEC) in the ground state, which should characterize the quasi-BEC in quantum double dark-soliton states that we assume to occur in the weak coupling regime. First, we show the exact time evolution of the density profile in the quantum state associated with a quantum double dark-soliton by the Bethe ansatz. Secondly, we derive a kind of macroscopic quantum wave-function effectively by exactly evaluating the square amplitude and phase profiles of the matrix element of the field operator between the quantum double dark-soliton states. The profiles are close to those of dark-solitons particularly in the weak-coupling regime. Then, the scattering of two notches in the quantum double dark-soliton state is exactly demonstrated. It is suggested from the above observations that the quasi-BEC should play a significant role in the dynamics of quantum double dark-soliton states. If the condensate fraction is close to 1, the quantum state should be well approximated by the quasi-BEC state where the mean-field picture is valid.
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Submitted 7 April, 2023; v1 submitted 1 July, 2022;
originally announced July 2022.
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Change of superconducting character in UTe2induced by magnetic field
Authors:
K. Kinjo,
H. Fujibayashi,
S. Kitagawa,
K. Ishida,
Y. Tokunaga,
H. Sakai,
S. Kambe,
A. Nakamura,
Y. Shimizu,
Y. Homma,
D. X. Li,
F. Honda,
D. Aoki,
K. Hiraki,
M. Kimata,
T. Sasaki
Abstract:
UTe2 is a recently discovered spin-triplet superconductor. One of the characteristic features of UTe2 is a magnetic field (H)-boosted superconductivity above 16 T when H is applied exactly parallel to the b axis. To date, this superconducting (SC) state has not been thoroughly investigated, and the SC properties as well as the spin state of this high-H SC (HHSC) phase are not well understood. In t…
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UTe2 is a recently discovered spin-triplet superconductor. One of the characteristic features of UTe2 is a magnetic field (H)-boosted superconductivity above 16 T when H is applied exactly parallel to the b axis. To date, this superconducting (SC) state has not been thoroughly investigated, and the SC properties as well as the spin state of this high-H SC (HHSC) phase are not well understood. In this study, we performed AC magnetic susceptibility and nuclear magnetic resonance (NMR) measurements and found that, up to 24.8 T, the HHSC state is intrinsic to UTe2 and quite sensitive to the H angle, and that its SC character is different from that in the low-H SC (LHSC) state. The dominant spin component of the spin-triplet pair is along the a axis in the LHSC state but is changed in the HHSC state along the b axis. Our results indicate that H-induced multiple SC states originate from the remaining spin degrees of freedom.
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Submitted 13 April, 2023; v1 submitted 6 June, 2022;
originally announced June 2022.
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Drastic change in magnetic anisotropy of UTe2 under pressure revealed by 125Te-NMR
Authors:
Katsuki Kinjo,
Hiroki Fujibayashi,
Genki Nakamine,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Dai Aoki
Abstract:
To investigate the normal-state magnetic properties of UTe2 under pressure, we perform 125Te nuclear magnetic resonance (NMR) measurements up to 2 GPa. Below 1.2 GPa, the b-axis NMR Knight shift shows a broad maximum at the so-called T_chimax on cooling, which is consistent with the magnetization measurement under pressure. T_chimax decreases with increasing pressure and disappears at the critical…
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To investigate the normal-state magnetic properties of UTe2 under pressure, we perform 125Te nuclear magnetic resonance (NMR) measurements up to 2 GPa. Below 1.2 GPa, the b-axis NMR Knight shift shows a broad maximum at the so-called T_chimax on cooling, which is consistent with the magnetization measurement under pressure. T_chimax decreases with increasing pressure and disappears at the critical pressure Pc = 1.7 GPa, above which superconductivity is destroyed. This tendency is also observed in the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1. At low pressures, 1/T1 shows a conventional Fermi-liquid behavior (1/T1T = constant) at low temperatures, indicating the formation of the heavy-fermion state. Above Pc, 1/T1T follows a 1/T behavior without any crossover to the heavy-fermion state down to the lowest temperature (~3 K). In addition, the NMR signals disappear below 3~K, due to the influence of the magnetically ordered moments. From the pressure dependence of the T_chimax and Knight shift, it was found that the Fermi surface character is abruptly changed at Pc, and that superconductivity is observed only in the heavy-fermion state.
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Submitted 24 March, 2022;
originally announced March 2022.
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Superconducting order parameter in UTe$_2$ determined by Knight shift measurement
Authors:
Hiroki Fujibayashi,
Genki Nakamine,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Dai Aoki
Abstract:
This study investigates the spin susceptibility in U-based superconductor UTe$_2$ in the superconducting (SC) state by using Knight shift measurements for a magnetic field $H$ along the $a$ axis, which is the magnetic easy axis of UTe$_2$. Although a tiny anomaly ascribed to the SC diamagnetic effect was observed just below the SC transition temperature $T_{\rm c}$, the $a$-axis Knight shift in th…
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This study investigates the spin susceptibility in U-based superconductor UTe$_2$ in the superconducting (SC) state by using Knight shift measurements for a magnetic field $H$ along the $a$ axis, which is the magnetic easy axis of UTe$_2$. Although a tiny anomaly ascribed to the SC diamagnetic effect was observed just below the SC transition temperature $T_{\rm c}$, the $a$-axis Knight shift in the SC state shows no significant decrease, following the extrapolation from the normal-state temperature dependence. This indicates that the spin susceptibility is nearly unchanged below $T_{\rm c}$. Considering the previous Knight shift results for $H \parallel b$ and $H \parallel c$, the dominant SC state is determined to be $B_{\rm 3u}$ in the spin-triplet pairing, which is consistent with the spin anisotropy in the normal state. The present result shows that UTe$_2$ is a spin-triplet superconductor with spin degrees of freedom.
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Submitted 18 March, 2022; v1 submitted 16 March, 2022;
originally announced March 2022.
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Two-dimensional XY-type Magnetic Properties of Locally Noncentrosymmetric Superconductor CeRh$_2$As$_2$
Authors:
Shunsaku Kitagawa,
Mayu Kibune,
Katsuki Kinjo,
Masahiro Manago,
Takanori Taniguchi,
Kenji Ishida,
Manuel Brando,
Elena Hassinger,
Christoph Geibel,
Seunghyun Khim
Abstract:
We performed $^{75}$As-NMR measurements to investigate the normal-state magnetic properties of CeRh$_2$As$_2$, a recently-discovered heavy-fermion superconductor. The magnitude and temperature dependence of the Knight shift at the As(2) site indicate easy-plane-type magnetic anisotropy in CeRh$_2$As$_2$. With regard to spin fluctuations, the temperature dependence of the nuclear spin-lattice relax…
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We performed $^{75}$As-NMR measurements to investigate the normal-state magnetic properties of CeRh$_2$As$_2$, a recently-discovered heavy-fermion superconductor. The magnitude and temperature dependence of the Knight shift at the As(2) site indicate easy-plane-type magnetic anisotropy in CeRh$_2$As$_2$. With regard to spin fluctuations, the temperature dependence of the nuclear spin-lattice relaxation rate $1/T_1$ arising from the 4$f$ electrons decreases from high-temperature constant behavior on cooling at $\sim$ 40~K, which is typical behavior of heavy-fermion systems. In addition, $1/T_1$ becomes constant at low temperatures, suggesting spatially two-dimensional antiferromagnetic fluctuations. Two-dimensional magnetic correlations in the real space are quite rare among heavy-fermion superconductors, and they may be a key factor in the unique superconducting multi-phase in CeRh$_2$As$_2$.
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Submitted 7 March, 2022;
originally announced March 2022.
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First-Order Antiferromagnetic Transition and Novel Gapless Excitation in a 4f Zigzag Chain Compound YbCuS2
Authors:
F. Hori,
K. Kinjo,
S. Kitagawa,
K. Ishida,
Yudai Ohmagari,
T. Onimaru
Abstract:
We report on the 63/65Cu-nuclear magnetic resonance and nuclear quadrupole resonance (NQR) studies of trivalent Yb zigzag chain compound YbCuS2. Sharp NQR signals were observed in the paramagnetic (PM) state. Below TO = 0.95 K, the multi peaks induced by the internal magnetic fields arising from the antferromagnetic (AFM) ordered moments appear and coexist with the PM signal down to 0.85 K, eviden…
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We report on the 63/65Cu-nuclear magnetic resonance and nuclear quadrupole resonance (NQR) studies of trivalent Yb zigzag chain compound YbCuS2. Sharp NQR signals were observed in the paramagnetic (PM) state. Below TO = 0.95 K, the multi peaks induced by the internal magnetic fields arising from the antferromagnetic (AFM) ordered moments appear and coexist with the PM signal down to 0.85 K, evidencing the first-order AFM phase transition at TO. In addition, the nuclear spin-lattice relaxation rate 1/T1 abruptly decreases below TO and shows the T-linear behavior below 0.5 K. The significant large 1/T1T value strongly suggests the presence of the novel gapless spin excitation in low temperature region.
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Submitted 19 January, 2022;
originally announced January 2022.
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Slow Electronic Dynamics in the Paramagnetic State of UTe$_2$
Authors:
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Yoshinori Haga,
Yoshifumi Tokiwa,
Petr Opletal,
Hiroki Fujibayashi,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Dai Aoki
Abstract:
$^{125}$Te NMR experiments in field ($H$) applied along the easy magnetization axis (the $a$-axis) revealed slow electronic dynamics developing in the paramagnetic state of UTe$_2$. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 30$-$40 K, where the spin susceptibility along the hard magnetization axis (the $b…
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$^{125}$Te NMR experiments in field ($H$) applied along the easy magnetization axis (the $a$-axis) revealed slow electronic dynamics developing in the paramagnetic state of UTe$_2$. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 30$-$40 K, where the spin susceptibility along the hard magnetization axis (the $b$-axis) shows a broad maximum. The experiments also imply that tiny amounts of disorder or defects locally disturb the long-range electronic correlations and develop an inhomogeneous electronic state at low temperatures, leading to a low temperature upturn observed in the bulk-susceptibility in $H\|a$. We suggest that UTe$_2$ would be located on the paramagnetic side near an electronic phase boundary, where either magnetic or Fermi-surface instability would be the origin of the characteristic fluctuations.
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Submitted 4 February, 2022; v1 submitted 19 January, 2022;
originally announced January 2022.
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Observation of antiferromagnetic order as odd-parity multipoles inside the superconducting phase in CeRh$_{2}$As$_{2}$
Authors:
Mayu Kibune,
Shunsaku Kitagawa,
Katsuki Kinjo,
Shiki Ogata,
Masahiro Manago,
Takanori Taniguchi,
Kenji Ishida,
Manuel Brando,
Elena Hassinger,
Helge Rosner,
Christoph Geibel,
Seunghyun Khim
Abstract:
Spatial inversion symmetry in crystal structures is closely related to the superconducting (SC) and magnetic properties of materials. Recently, several theoretical proposals that predict various interesting phenomena caused by the breaking of the local inversion symmetry have been presented. However, experimental validation has not yet progressed owing to the lack of model materials. Here we prese…
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Spatial inversion symmetry in crystal structures is closely related to the superconducting (SC) and magnetic properties of materials. Recently, several theoretical proposals that predict various interesting phenomena caused by the breaking of the local inversion symmetry have been presented. However, experimental validation has not yet progressed owing to the lack of model materials. Here we present evidence for antiferromagnetic (AFM) order in CeRh$_{2}$As$_{2}$ (SC transition temperature $T_{\rm SC} \sim 0.37$~K), wherein the Ce site breaks the local inversion symmetry. The evidence is based on the observation of different extents of broadening of the nuclear quadrupole resonance spectrum at two crystallographically inequivalent As sites. This AFM ordering breaks the inversion symmetry of this system, resulting in the activation of an odd-parity magnetic multipole. Moreover, the onset of antiferromagnetism $T_{\rm N}$ within an SC phase, with $T_{\rm N} < T_{\rm SC}$, is quite unusual in systems wherein superconductivity coexists or competes with magnetism. Our observations show that CeRh$_{2}$As$_{2}$ is a promising system to study how the absence of local inversion symmetry induces or influences unconventional magnetic and SC states, as well as their interaction.
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Submitted 13 December, 2021;
originally announced December 2021.
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Quantum dark solitons in the 1D Bose gas: From single to double dark-solitons
Authors:
Kayo Kinjo,
Eriko Kaminishi,
Takashi Mori,
Jun Sato,
Rina Kanamoto,
Tetsuo Deguchi
Abstract:
We study quantum double dark-solitons by constructing corresponding quantum states in the Lieb-Liniger model for the one-dimensional Bose gas. Here we expect that the Gross-Pitaevskii (GP) equation should play a central role in the long distance mean-field behavior of the 1D Bose gas. We first introduce novel quantum states of a single dark soliton with a nonzero winding number. We show them by ex…
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We study quantum double dark-solitons by constructing corresponding quantum states in the Lieb-Liniger model for the one-dimensional Bose gas. Here we expect that the Gross-Pitaevskii (GP) equation should play a central role in the long distance mean-field behavior of the 1D Bose gas. We first introduce novel quantum states of a single dark soliton with a nonzero winding number. We show them by exactly evaluating not only the density profile but also the profiles of the square amplitude and phase of the matrix element of the field operator between the $N$-particle and $(N-1)$-particle states. For elliptic double dark-solitons, the density and phase profiles of the corresponding states almost perfectly agree with those of the classical solutions, respectively, in the weak coupling regime. We then show that the scheme of the mean-field product state is quite effective for the quantum states of double dark solitons. Assigning the ideal Gaussian weights to a sum of the excited states with two particle-hole excitations we obtain double dark-solitons of distinct narrow notches with different depths. We suggest that the mean-field product state should be well approximated by the ideal Gaussian weighted sum of the low excited states with a pair of particle-hole excitations. The results of double dark-solitons should be fundamental and useful for constructing quantum multiple dark-solitons.
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Submitted 4 November, 2021;
originally announced November 2021.
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Inhomogeneous Superconducting State Probed by $^{125}$Te NMR on UTe$_2
Authors:
Genki Nakamine,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Dai Aoki
Abstract:
UTe$_2$ is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. To detect these degrees of freedom and obtain the solid evidence of spin-triplet superconductivity in UTe$_2$, we performed $^{125}$Te-NMR measurement. We previously…
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UTe$_2$ is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. To detect these degrees of freedom and obtain the solid evidence of spin-triplet superconductivity in UTe$_2$, we performed $^{125}$Te-NMR measurement. We previously reported that the shoulder signal appears in NMR spectra below the superconducting (SC) transition temperature $T_{\rm c}$ in $H \parallel b$, and that a slight decrease in the Knight shift along the $b$ and $c$ axes ($K_b$ and $K_c$, respectively) below $T_{\rm c}$ at a low magnetic field $H$. To clarify the origin of the shoulder signal and the trace of the decrease in $K_b$, we compared the $^{125}$Te-NMR spectra obtained when $H~\parallel~b$ and $H~\parallel~c$ and measured the $^{125}$Te-NMR spectra for $H~\parallel~b$ up to 14.5~T. The intensity of the shoulder signal observed for $H~\parallel~b$ has a maximum at $\sim 6$~T and vanishes above 10~T, although the superconductivity is confirmed by the $χ_{\rm AC}$ measurements, which can survive up to 14.5~T (maximum $H$ in the present measurement). Moreover, the decrease in $K_b$ in the SC state starts to be small around 7~T and almost zero at 12.5~T. This indicates that the SC spin state gradually changes with the application of $H$. Meanwhile, in $H~\parallel~c$, unexpected broadening without the shoulder signals was observed below $T_{\rm c}$ at 1~T, and this broadening was quickly suppressed with increasing $H$. We construct the $H$--$T$ phase diagram for $H~\parallel~b$ and $H~\parallel~c$ based on the NMR measurements and discuss possible SC states with the theoretical consideration. We suggest that the inhomogeneous SC state characterized by the broadening of the NMR spectrum originates from the spin degrees of freedom.
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Submitted 25 May, 2021;
originally announced May 2021.
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Anisotropic response of spin susceptibility in the superconducting state of UTe$_2$ probed with $^{125}$Te-NMR measurement
Authors:
Genki Nakamine,
Katsuki Kinjo,
Shunsaku Kitagawa,
Kenji Ishida,
Yo Tokunaga,
Hironori Sakai,
Shinsaku Kambe,
Ai Nakamura,
Yusei Shimizu,
Yoshiya Homma,
Dexin Li,
Fuminori Honda,
Dai Aoki
Abstract:
To investigate spin susceptibility in a superconducting (SC) state, we measured the $^{125}$Te-nuclear magnetic resonance (NMR) Knight shifts at magnetic fields ($H$) up to 6.5 T along the $b$ and $c$ axes of single-crystal UTe$_2$, a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the $b$ and $c$ axes ($K_b$ and $K_c$, respectively) decreased slight…
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To investigate spin susceptibility in a superconducting (SC) state, we measured the $^{125}$Te-nuclear magnetic resonance (NMR) Knight shifts at magnetic fields ($H$) up to 6.5 T along the $b$ and $c$ axes of single-crystal UTe$_2$, a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the $b$ and $c$ axes ($K_b$ and $K_c$, respectively) decreased slightly and the decrease in $K_b$ was almost constant up to 6.5 T. The reduction in $K_c$ decreased with increasing $H$, and $K_c$ was unchanged through the SC transition temperature at 5.5 T, excluding the possibility of spin-singlet pairing. Our results indicate that spin susceptibilities along the $b$ and $c$ axes slightly decrease in the SC state in low $H$, and the $H$ response of SC spin susceptibility is anisotropic in the $bc$ plane. We discuss the possible $d$-vector state within the spin-triplet scenario and suggest that the dominant $d$-vector component for the case of $H \parallel b$ changes above 13 T, where $T_{\rm c}$ increases with increasing $H$.
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Submitted 4 March, 2021;
originally announced March 2021.
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Magnetic Field Effect on s-wave Superconductor LaRu4P12 Studied by 31P-NMR
Authors:
Katsuki Kinjo,
Shunsaku Kitagawa,
Yusuke Nakai,
Kenji Ishida,
Hitoshi Sugawara,
Hideyuki Sato
Abstract:
We have performed 31P-NMR measurements on the s-wave superconductor LaRu4P12 to investigate the magnetic field effect of the nuclear spin-lattice relaxation rate 1/T1 on a conventional full-gap superconductor. With increasing magnetic field, the Hebel-Slichter peak immediately below Tc in 1=T1 was suppressed, and the magnetic field dependence of 1/T1 at 0.8 K, well below Tc, was proportional to H2…
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We have performed 31P-NMR measurements on the s-wave superconductor LaRu4P12 to investigate the magnetic field effect of the nuclear spin-lattice relaxation rate 1/T1 on a conventional full-gap superconductor. With increasing magnetic field, the Hebel-Slichter peak immediately below Tc in 1=T1 was suppressed, and the magnetic field dependence of 1/T1 at 0.8 K, well below Tc, was proportional to H2. These behaviors can be fully understood by the orbital pair-breaking effect in a single-band s-wave superconductor
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Submitted 7 June, 2019; v1 submitted 2 June, 2019;
originally announced June 2019.