arXiv subjects

W. P. Beyermann

Publications and source records attributed to W. P. Beyermann.

8 recordsLinked to original sources

arXiv2026

Evidence of length scale effect in contact electrification in conducting thin film heterostructures

Contact electrification between two conducting materials is expected to exhibit length scale effect because the screening effect will diminish in conductors as a function of material dimensions. As a consequence, the interfacial charge accumulation will diffuse away from interface/surface to a critical penetration depth as a function of material dimension. This work experimentally demonstrates the length scale effect in a permalloy and degenerately doped p-Si heterostructure system due to the flexoelectricity mediated contact electrification. The contact electrification induced interlayer charge transfer is observed through the whole thickness in case of 400 nm thick p-Si samples. Whereas, the charge carrier diffuses to a depth of 51 nm from the interface in case of 2 um thick Si. The length scale effect also leads to metal-insulator transition in p-Si layers in both cases. These results present a new opportunity to tailor the physical properties in conducting materials using contact electrification.

cond-mat.mes-hall↗

arXiv2024

Oscillatory Hall effect from magnetoelectronic coupling in flexoelectronic silicon

The magnetoelectronic coupling can be defined as cross-domain coupling between electronic and magnetic properties, where modulation in magnetic properties changes the electronic properties. In this letter, an explicit experimental evidence of magnetoelectronic coupling is presented, which is uncovered from oscillatory Hall effect response in Hall measurement. The strain gradient in a MgO (1.8 nm)/p-Si (~400 nm) freestanding sample leads to transfer of electrons (~5X10^18 cm^-3) from valence to conduction band due to flexoelectronic charge separation in the p-Si layer. The resulting flexoelectronic polarization gives rise to temporal magnetic moment from dynamical multiferroicity. The external magnetic field changes the net temporal magnetic moment, which causes modulations in charge carrier concentration and oscillatory Hall effect. The period of oscillatory Hall response is 1.12 T, which is attributed to the magnitude of temporal magnetic moment. The discovery of oscillatory Hall effect adds a new member to the family of Hall effects.

cond-mat.mes-hall↗

arXiv2021

Experimental evidence of hidden spin polarization in silicon by using strain gradient

The centrosymmetric materials with hidden spin polarization are considered to be the promising candidates for realization of energy efficient spintronics systems and devices. However, the control of hidden spin polarization and resulting transport behavior is not well understood. We hypothesized that inhomogeneous strain can be the external knob to study and control hidden spin polarization. In this work, we demonstrate a strain gradient mediated symmetry breaking to discover the hidden spin polarization in centrosymmetric Si lattice. The hidden spin polarization gives rise to magnetocrystalline anisotropy and local magnetic moment along <111> directions in the Si. The local magnetic moment gives rise to spin-acoustic phonon coupling, which is the underlying cause of observed spin-Hall effect in both n-Si and p-Si. Discovery of hidden magnetic moment in Si not only challenges the fundamental understanding of the origin of the magnetism but also presents a giant leap in realization of spintronics systems.

cond-mat.mes-hall↗

arXiv2020

Flexoelectric effect mediated spin-to-charge conversion at amorphous-Si thin film interfaces

Interfacial spin to charge conversion arises due to an electric potential perpendicular to the interface. The electric potential can be artificially induced, for example, using ferroelectric and piezoelectric thin films at the interface. An alternate way to induce the electric potential could be flexoelectric field. The flexoelectricity can be observed in all the material that either have or lack inversion symmetry, additionally no large gate bias is needed. In this experimental study, we report large spin to charge conversion (spin-Hall angle- 0.578) at Ni80Fe20/amorphous-Si interfaces attributed to flexoelectricity mediated Rashba spin-orbit coupling. The flexoelectricity at the interface also gave rise to interlayer spin-acoustic phonon or flexo-magnetoelastic coupling. In addition to spin-charge conversion, the strained interfaces also led to almost three-fold increase in anomalous Nernst effect. This strain engineering for spin dependent thermoelectric behavior at room temperature opens a new window to the realization of spintronics and spin-caloritronics devices.

cond-mat.mes-hall↗

arXiv2020

Large spin-Hall effect in Si at room temperature

Silicon's weak intrinsic spin-orbit coupling and centrosymmetric crystal structure are a critical bottleneck to the development of Si spintronics, because they lead to an insignificant spin-Hall effect (spin current generation) and inverse spin-Hall effect (spin current detection). Here, we undertake current, magnetic field, crystallography dependent magnetoresistance and magneto thermal transport measurements to study the spin transport behavior in freestanding Si thin films. We observe a large spin-Hall magnetoresistance in both p-Si and n-Si at room temperature and it is an order of magnitude larger than that of Pt. One explanation of the unexpectedly large and efficient spin-Hall effect is spin-phonon coupling instead of spin-orbit coupling. The macroscopic origin of the spin-phonon coupling can be large strain gradients that can exist in the freestanding Si films. This discovery in a light, earth abundant and centrosymmetric material opens a new path of strain engineering to achieve spin dependent properties in technologically highly-developed materials.

cond-mat.mes-hall↗

arXiv2017

Spin mediated magneto-electro-thermal transport behavior in Ni80Fe20/MgO/p-Si thin films

In Si, spin-phonon interaction is the primary spin relaxation mechanism. At low temperatures, the absence of spin-phonon relaxation will lead to enhanced spin accumulation. Spin accumulation may change the electro-thermal transport within the material, and thus may serve as an investigative tool for characterizing spin-mediated behavior. Here we present the first experimental proof of spin accumulation induced electro-thermal transport behavior in a Pd (1 nm)/Ni80Fe20 (25 nm)/MgO (1 nm)/p-Si (2 um) specimen. The spin accumulation originates from the spin-Hall effect. The spin accumulation changes the phononic thermal transport in p-Si causing the observed magneto-electro-thermal transport behavior. We also observe the inverted switching behavior in magnetoresistance measurement at low temperatures in contrast to magnetic characterization, which is attributed to the canted spin states in p-Si due to spin accumulation. The spin accumulation is elucidated by current dependent anomalous Hall resistance measurement, which shows a decrease as the electric current is increased. This result may open a new paradigm in the field of spin-mediated transport behavior in semiconductor and semiconductor spintronics.

cond-mat.mes-hall↗

arXiv2009

Penetration depth, multiband superconductivity, and absence of muon-induced perturbation in superconducting PrOs$_{4}$Sb$_{12}$

Transverse-field muon spin rotation ($μ$SR) experiments in the heavy-fermion superconductor PrOs$_{4}$Sb$_{12}$ ($T_{c}=1.85$ K) suggest that the superconducting penetration depth $λ(T)$ is temperature-independent at low temperatures, consistent with a gapped quasiparticle excitation spectrum. In contrast, radiofrequency (rf) inductive measurements yield a stronger temperature dependence of $λ(T)$, indicative of point nodes in the gap. This discrepancy appears to be related to the multiband structure of PrOs$_{4}$Sb$_{12}$. Muon Knight shift measurements in PrOs$_{4}$Sb$_{12}$ suggest that the perturbing effect of the muon charge on the neighboring Pr$^{3+}$ crystalline electric field is negligibly small, and therefore is unlikely to cause the difference between the $μ$SR and rf results.

cond-mat.supr-con↗

arXiv1999

Magnetic Field Dependence of the Low-Temperature Specific Heat in PrInAg_2: Support for a Non-Magnetic Heavy-Fermion Ground State

In order to elucidate the nature of the ground state in the heavy-electron system PrInAg_2, we measured its specific heat for temperatures between 60 mK and 2 K in magnetic fields up to 9 T. The peak maximum of the low temperature anomaly in the specific heat (interpreted as Kondo anomaly) shifts from 0.42 K at zero field to 0.45 K at 6 T, and to 0.5 K at 9 T. The data at 3 T (after subtracting the low temperature tail due to a Schottky anomaly) is practically indistinguishable from the zero field data. A low temperature nuclear Schottky anomaly from a hyperfine enhancement of the Pr nuclei was observed in field. Both enhanced hyperfine interaction and the insensitivity of the specific heat anomaly to fields support the hypothesis that the Kondo effect in this system has a non-magnetic origin.

cond-mat.str-el↗