Measurement of magnetic susceptibility in pulsed magnetic fields using a proximity detector oscillator

Quantum Interference between Quasi-2D Fermi Surface Sheets in UTe_{2}

UTe_{2} is a spin-triplet superconductor candidate for which high quality samples with long mean free paths have recently become available, enabling quantum oscillation measurements to probe its Fermi surface and effective carrier masses. It has recently been reported that UTe_{2} possesses a 3D Fermi surface component [Phys. Rev. Lett. 131, 036501 (2023)PRLTAO0031-900710.1103/PhysRevLett.131.036501]. The distinction between 2D and 3D Fermi surface sections in triplet superconductors can have important implications regarding the topological properties of the superconductivity. Here we report the observation of oscillatory components in the magnetoconductance of UTe_{2} at high magnetic fields. We find that these oscillations are well described by quantum interference between quasiparticles traversing semiclassical trajectories spanning magnetic breakdown networks. Our observations are consistent with a quasi-2D model of this material's Fermi surface based on prior dHvA-effect measurements. Our results strongly indicate that UTe_{2}-which exhibits a multitude of complex physical phenomena-possesses a remarkably simple Fermi surface consisting exclusively of two quasi-2D cylindrical sections.

Sudden adiabaticity signals reentrant bulk superconductivity in UTe2

There has been a recent surge of interest in UTe2 due to its unconventional magnetic field (H)-reinforced spin-triplet superconducting phases persisting at fields far above the simple Pauli limit for H ∥ [ 010 ] . Magnetic fields in excess of 35 T then induce a field-polarized magnetic state via a first-order-like phase transition. More controversially, for field orientations close to H ∥ [ 011 ] and above 40 T, electrical resistivity measurements suggest that a further superconducting state may exist. However, no Meissner effect or thermodynamic evidence exists to date for this phase making it difficult to exclude alternative scenarios. In this paper, we describe a study using thermal, electrical, and magnetic probes in magnetic fields of up to 55 T applied between the [010] (b) and [001] (c) directions. Our MHz conductivity data reveal the field-induced state of low or vanishing electrical resistance; our simultaneous magnetocaloric effect measurements (i.e. changes in sample temperature due to changing magnetic field) show the first definitive evidence for adiabaticity and thermal behavior characteristic of bulk field-induced superconductivity.

Piston-cylinder cell made of Ni-Cr-Al alloy for magnetic susceptibility measurements under high pressures in pulsed high magnetic fields

We developed a metallic pressure cell made of 56Ni-40Cr-4Al (Ni-Cr-Al) alloy for use with a non-destructive pulse magnet and a magnetic susceptibility measurement apparatus with a proximity detector oscillator (PDO) in pulsed magnetic fields of up to 51 T under pressures of up to 2.1 GPa. Both the sample and sensor coil of the PDO were placed in the cell so that the magnetic signal from Ni-Cr-Al would not overlay the intrinsic magnetic susceptibility of the sample. A systematic investigation of the Joule heating originating from metallic parts of the pressure cell revealed that the increase in sample temperature is negligible at 1.4 K in magnetic fields of up to 40 T in the field-ascending process for the maximum applied magnetic field of 51 T. The effectiveness of our apparatus was demonstrated by investigating the pressure dependence of the magnetization process of the triangular-lattice antiferromagnet Ba3CoSb2O9.

Emergent charge order in pressurized kagome superconductor CsV3Sb5

The discovery of several electronic orders in kagome superconductors AV₃Sb₅ (A means K, Rb, Cs) provides a promising platform for exploring unprecedented emergent physics^1-9. Under moderate pressure (<2.2 GPa), the triple-Q charge density wave (CDW) order is monotonically suppressed by pressure, while the superconductivity shows a two-dome-like behaviour, suggesting an unusual interplay between superconductivity and CDW order^10,11. Given that time-reversal symmetry breaking and electronic nematicity have been revealed inside the triple-Q CDW phase^8,9,12,13, understanding this CDW order and its interplay with superconductivity becomes one of the core questions in AV₃Sb₅ (refs. ^3,5,6). Here, we report the evolution of CDW and superconductivity with pressure in CsV₃Sb₅ by ⁵¹V nuclear magnetic resonance measurements. An emergent CDW phase, ascribed to a possible stripe-like CDW order with a unidirectional 4a₀ modulation, is observed between P_c1 ≅ 0.58 GPa and P_c2 ≅ 2.0 GPa, which explains the two-dome-like superconducting behaviour under pressure. Furthermore, the nuclear spin-lattice relaxation measurement reveals evidence for pressure-independent charge fluctuations above the CDW transition temperature and unconventional superconducting pairing above P_c2. Our results not only shed new light on the interplay of superconductivity and CDW, but also reveal new electronic correlation effects in kagome superconductors AV₃Sb₅.

Inductive temperature measurement: A new sensor improvement for industrial applications

A remote temperature sensing technique was developed by measuring exponential decay current pulses in a Helmholtz coil. After an initial calibration to extract a mathematical function relating the time constant (τ) to the temperature of the object sensed, the temperature of other similar objects can be estimated with less power, less strict positioning of the object, and more sensitivity than previous techniques, even inside a water-based fluid.

Measurement of the magnetic susceptibility of subtle paramagnetic solutions using the diamagnetic repulsion of polymer microparticles

Herein, we described a microfluidic device that enabled the measurement of magnetic susceptibility of a subtle paramagnetic solution that could not be determined by conventional magnetic susceptibility measurement methods such as a superconducting quantum interference device (SQUID). We measured the diamagnetic repelling velocity of polystyrene microparticles suspended in a weak paramagnetic solution including 50-150 mM of gadolinium-diethylenetriamine penta-acetic acid (GD-DTPA) and superparamagnetic iron oxide nanoparticles (SPION) (10 nm in diameter) dispersed in distilled water at various concentrations. The measured diamagnetic repelling velocities correlated with our prediction and also with the magnetic susceptibility of the SPION solution measured by a SQUID magnetometer. Via this approach, we could determine the magnetic susceptibility of the subtle paramagnetic solution of GD-DTPA that could not be measured via the conventional method. This study provides us with the new capability of analyzing weakly paramagnetic solutions such as paramagnetic components or metal contaminants present in environmental liquid samples at low concentrations.

Phase-sensitive dynamic susceptibility setup for measurements in pulsed magnetic fields

Dynamic susceptibility, commonly referred to as AC susceptibility, χ_AC, is a powerful tool to characterize a material's magnetic properties in the presence of a magnetic field B, such as magnetic ordering or spin-relaxation phenomena. The standard technique for accessing χ_AC is based on measurements of the voltage which is induced in a coil by changes of a sample's magnetization in response to a small oscillating magnetic field. Importantly, this setup allows for a phase-sensitive detection of the susceptibility, thereby providing information on the magnetization dynamics. This method is frequently used in the low-field range, up to several Tesla, where DC fields are readily available. However, there is a growing demand for such magnetic measurements at higher fields, conveniently accessible by the use of pulse-field technology. Whereas various techniques are available for measuring the in-phase part of the susceptibility χ_AC ^', none of them allows for the determination of the out-of-phase part χ_AC ^″. Here we present a realization of an AC susceptometer for measurements of both the in- and out-of-phase component at frequencies up to 47 kHz and an oscillating amplitude of 1.5 mT in a pulsed magnetic field. With this setup, a magnetic signal of 3.6 × 10^-6 emu can be resolved. As the setup also enables susceptibility measurements to be performed before and after the field pulse, it can be used to detect temperature changes in response to changes of the magnetic field. This will be demonstrated by measurements on the low-dimensional spin-1/2 system CuSO₄·5H₂O.

Extreme magnetic field-boosted superconductivity

Applied magnetic fields underlie exotic quantum states, such as the fractional quantum Hall effect¹ and Bose-Einstein condensation of spin excitations². Superconductivity, however, is inherently antagonistic towards magnetic fields. Only in rare cases^3-5 can these effects be mitigated over limited fields, leading to re-entrant superconductivity. Here, we report the coexistence of multiple high-field re-entrant superconducting phases in the spin-triplet superconductor UTe₂ (ref. ⁶). We observe superconductivity in the highest magnetic field range identified for any re-entrant superconductor, beyond 65 T. Although the stability of superconductivity in these high magnetic fields challenges current theoretical models, these extreme properties seem to reflect a new kind of exotic superconductivity rooted in magnetic fluctuations⁷ and boosted by a quantum dimensional crossover⁸.

Quantum oscillations of electrical resistivity in an insulator

In metals, orbital motions of conduction electrons on the Fermi surface are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau quantization is generally absent in insulators. Here, we report a notable exception in an insulator-ytterbium dodecaboride (YbB₁₂). The resistivity of YbB₁₂, which is of a much larger magnitude than the resistivity in metals, exhibits distinct quantum oscillations. These unconventional oscillations arise from the insulating bulk, even though the temperature dependence of the oscillation amplitude follows the conventional Fermi liquid theory of metals with a large effective mass. Quantum oscillations in the magnetic torque are also observed, albeit with a lighter effective mass.

Giant Pressure Dependence and Dimensionality Switching in a Metal-Organic Quantum Antiferromagnet

We report an extraordinary pressure dependence of the magnetic interactions in the metal-organic system [CuF_{2}(H_{2}O)_{2}]_{2}pyrazine. At zero pressure, this material realizes a quasi-two-dimensional spin-1/2 square-lattice Heisenberg antiferromagnet. By high-pressure, high-field susceptibility measurements we show that the dominant exchange parameter is reduced continuously by a factor of 2 on compression. Above 18 kbar, a phase transition occurs, inducing an orbital re-ordering that switches the dimensionality, transforming the quasi-two-dimensional lattice into weakly coupled chains. We explain the microscopic mechanisms for both phenomena by combining detailed x-ray and neutron diffraction studies with quantitative modeling using spin-polarized density functional theory.

Spin susceptibility of charge-ordered YBa2Cu3O y across the upper critical field

The value of the upper critical field H_c2, a fundamental characteristic of the superconducting state, has been subject to strong controversy in high-T_c copper oxides. Since the issue has been tackled almost exclusively by macroscopic techniques so far, there is a clear need for local-probe measurements. Here, we use ¹⁷O NMR to measure the spin susceptibility [Formula: see text] of the CuO₂ planes at low temperature in charge-ordered YBa₂Cu₃O _y We find that [Formula: see text] increases (most likely linearly) with magnetic field H and saturates above field values ranging from 20 T to 40 T. This result is consistent with the lowest H_c2 values claimed previously and with the interpretation that the charge density wave (CDW) reduces H_c2 in underdoped YBa₂Cu₃O _y Furthermore, the absence of marked deviation in [Formula: see text] at the onset of long-range CDW order indicates that this [Formula: see text] reduction and the Fermi-surface reconstruction are primarily rooted in the short-range CDW order already present in zero field, not in the field-induced long-range CDW order. Above [Formula: see text], the relatively low values of [Formula: see text] at [Formula: see text] K show that the pseudogap is a ground-state property, independent of the superconducting gap.

Note: radio frequency inductance-capacitance band-stop filter circuit to perform contactless conductivity measurements in pulsed magnetic fields

We present a new technique to perform radio frequency (rf) contactless conductivity measurements in pulsed magnetic fields to probe different ground states in condensed matter physics. The new method utilizes a simple analog band-stop filter circuit implemented in a radio frequency transmission setup to perform contactless conductivity measurements. The new method is more sensitive than the other methods (e.g., the tunnel diode oscillator and the proximity detector oscillator) due to more sensitive dependence of the circuit resonance frequency on the tank circuit inductance (not the transmission line). More important, the new method is more robust than other methods when used to perform measurements in very high magnetic fields, works for a wide range of temperatures (i.e., 300 K-1.4 K) and is less sensitive to noise and mechanical vibrations during pulse magnet operation. The new technique was successfully applied to measure the Shubnikov-de Haas effect in Bi(2)Se(3) in pulsed magnetic fields of up to 60 T.