arXiv subjects

William P. Halperin

Publications and source records attributed to William P. Halperin.

5 recordsLinked to original sources

arXiv2025

Nuclear spin coherence in superconducting Nb$_3$Sn

We have investigated the normal and superconducting states of the technologically important compound Nb$_3$Sn using $^{93}$Nb nuclear magnetic resonance. From spin-lattice relaxation we find strong suppression of the zero-temperature superconducting order parameter by magnetic field. Additionally we have identified an anomalously large electron-nuclear exchange interaction from spin-spin relaxation measurements, an order of magnitude beyond that of the nuclear dipolar coupling. This RKKY interaction evolves from normal to superconducting states, becoming essentially Lorentzian in the low temperature limit.

cond-mat.supr-con↗

arXiv2023

Nuclear Magnetic Resonance Investigation of Superconducting and Normal State Nb$_3$Sn

The superconductor Nb$_3$Sn has a high critical temperature and high critical field, widely used for high-field superconducting magnets. In this work we investigate its microscopic electronic structure with $^{93}$Nb nuclear magnetic resonance (NMR). The high-quality Nb$_3$Sn powder sample was studied in both 3.2T and 7T magnetic fields in the temperature range from 1.5K to 300K. From measurement of the spectrum and its theoretical analysis, we find evidence for anisotropy despite its cubic crystal structure. This anisotropy is manifest in alignment of powder grains under certain temperature and field cycling conditions. The Knight shift and spin-lattice relaxation rate, $T_1^{-1}$, were measured in the normal state. Additionally, $T_1^{-1}$ was measured in the superconducting state and compared with BCS theory revealing a weak field dependence, with an energy gap $Δ(0)=2.0\pm0.08k_B T_c$ at 3.2T and $Δ(0)=1.73\pm0.08k_B T_c$ at 7T, indicating suppression of the order parameter by magnetic field.

cond-mat.supr-con↗

arXiv2022

Contactless Excitation of Acoustic Resonance in Insulating Wafers

Contactless excitation and detection of high harmonic acoustic overtones in a thin insulator single crystal are described using radio frequency spectroscopy techniques. Single crystal [001] silicon wafer samples were investigated, one side covered with a Nb thin film, the common starting point for fabrication of quantum devices. The coupling between electromagnetic signals and mechanical oscillation is achieved from the Lorentz force generated by an external magnetic field. This method is suitable for any sample with a metallic surface or covered with a thin metal film. High resolution measurements of the temperature dependence of the sound velocity and elastic constants of silicon are reported and compared with known results.

physics.app-ph↗

arXiv2021

RKKY coupled local moment magnetism in NaFe$_{1-x}$Cu$_{x}$As

A central question in a large class of strongly correlated electron systems, including heavy fermion compounds and iron pnictides, is the identification of different phases and their origins. It has been shown that the antiferromagnetic (AFM) phase in some heavy fermion compounds is induced by Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized moments, and that the competition between this interaction and Kondo effect is responsible for quantum criticality. However, conclusive experimental evidence of the RKKY interaction in pnictides is lacking. Here, using high resolution $^{23}$Na NMR measurements on lightly Cu-doped metallic single crystals of NaFe$_{1-x}$Cu$_{x}$As ~($x \approx 0.01$) and numerical simulation, we show direct evidence of the RKKY interaction in this pnictide system. Aided by computer simulation, we identify the $^{23}$Na NMR satellite resonances with the RKKY oscillations of spin polarization at Fe sites. Our $^{23}$Na spin-lattice and spin-spin relaxation data exhibits signature of an itinerant and inhomogeneous AFM phase in this system, accompanied by a simulation of Cu-induced perturbation to the ordered moments on the Fe sites. Our NMR results indicate coexistence of local and itinerant magnetism in lightly Cu-doped NaFe$_{1-x}$Cu$_{x}$As.

cond-mat.str-el↗

arXiv2017

Grand Challenges in Quantum Fluids and Solids

We present a short review of the current and recent development in the field of superfluid 3He and 4He. The review is based on the topics discussed at the NSF sponsoredWorkshop on Grand Challenges in Quantum Fluids and Solids chaired by Moses Chan from Pennsylvania State University and held at University of Buffalo in August, 2015.

cond-mat.other↗