arXiv subjects

Mariusz Ciorga

Publications and source records attributed to Mariusz Ciorga.

14 recordsLinked to original sources

arXiv2025

The impact of electrical contacts on the optical properties of a MoS$_{2}$ monolayer

Achieving high performance in transition-metal-dichalcogenide-based optoelectronic devices is challenging -- the realization of an efficient electrical contacting scheme should not be obtained at the expense of their optical quality. Here we present the optical properties of MoS$_{2}$ monolayers which have been electrically contacted with bismuth and gold. The photoluminescence (PL) spectrum of the samples contacted with both materials is significantly broadened. In the case of the bismuth contacted sample we note an additional, low energy band in the PL spectrum, attributed to a defect state formed during the evaporation of Bi. Comparing the intensity of the excitonic peak and of the defect-related peak, we note that there is a correlation between the type of contacts and the optical properties.

cond-mat.mes-hall↗

arXiv2025

Spin injection and detection in all-van der Waals 2D devices

In this work we report efficient out-of-plane spin injection and detection in an all-van der Waals based heterostructure using only exfoliated 2D materials. We demonstrate spin injection by measuring spin-valve and Hanle signals in non-local transport in a stack of Fe$_3$GeTe$_2$ (FGT), hexagonal boron nitride (hBN) and graphene layers. FGT flakes form the spin aligning electrodes necessary to inject and detect spins in the graphene channel. The hBN tunnel barrier provides a high-quality interface between the ferromagnetic electrodes and graphene, eliminating the conductivity mismatch problem, thus ensuring efficient spin injection and detection with spin injection efficiencies of up to $P=40$\%. Our results demonstrate that FGT/hBN/graphene heterostructures form a promising platform for realizing 2D van der Waals spintronic devices.

cond-mat.mes-hall↗

arXiv2025

Study of gold and bismuth electrical contacts to a MoS$_{2}$ monolayer

Semiconducting transition metal dichalcogenides (TMDCs) present new possibilities for designing novel electronic devices. An efficient contacting scheme is required to take advantage of exceptional opto-electronic properties of TMDCs in future electronic devices. This is however challenging for TMDCs, mostly due to the typically high Schottky barrier formed between a metal and a semiconductor. Here we investigate different approaches for contacting MoS$_{2}$, utilizing both metallic gold and semimetallic bismuth as contact materials. The collected I-V characteristics of Bi-contacted devices are compared with the performance of traditional gold contacts. The method of AFM ironing, which we used to enhance the parameters of gold contacts, is also described. Additionally, we show preliminary results regarding an optical response for both types of samples.

cond-mat.mes-hall↗

arXiv2024

Approaching the Intrinsic Properties of Moiré Structures Using Atomic Force Microscopy Ironing

Stacking monolayers of transition metal dichalcogenides (TMDs) has led to the discovery of a plethora of new exotic phenomena, resulting from moiré pattern formation. Due to the atomic thickness and high surface-to-volume ratio of heterostructures, the interfaces play a crucial role. Fluctuations in the interlayer distance affect interlayer coupling and moiré effects. Therefore, to access the intrinsic properties of the TMD stack, it is essential to obtain a clean and uniform interface between the layers. Here, we show that this is achieved by ironing with the tip of an atomic force microscope. This post-stacking procedure dramatically improves the homogeneity of the interfaces, which is reflected in the optical response of the interlayer exciton. We demonstrate that ironing improves the layer coupling, enhancing moiré effects and reducing disorder. This is crucial for the investigation of TMD heterostructure physics, which currently suffers from low reproducibility.

cond-mat.mes-hall↗

arXiv2023

Controlled rotation of electrically injected spins in a non-ballistic spin field-effect transistor

Electrically controlled rotation of spins in a semiconducting channel is a prerequisite for the successful realization of many spintronic devices, like, e.g., the spin field effect transistor (sFET). To date, there have been only a few reports on electrically controlled spin precession in sFET-like devices. These devices operated in the ballistic regime, as postulated in the original sFET proposal, and hence need high SOC channel materials in practice. Here, we demonstrate gate-controlled precession of spins in a non-ballistic sFET using an array of narrow diffusive wires as a channel between a spin source and a spin drain. Our study shows that spins traveling in a semiconducting channel can be coherently rotated on a distance far exceeding the electrons mean free path, and spin-transistor functionality can be thus achieved in non-ballistic channels with relatively low SOC, relaxing two major constraints of the original sFET proposal.

cond-mat.mes-hall↗

arXiv2017

Gate-tunable large magnetoresistance in an all-semiconductor spin-transistor-like device

A large spin-dependent and electric field-tunable magnetoresistance of a two-dimensional electron system (2DES) is a key ingredient for the realization of many novel concepts for spin-based electronic devices. The low magnetoresistance observed during the last decades in devices with lateral semiconducting (SC) transport channels between ferromagnetic (FM) source (S) and drain (D) contacts has been the main obstacle for realizing spin field effect transistor proposals. Here, we show both, a large two terminal magnetoresistance in lateral 2DES-based spin valve geometry, with up to 80% resistance change, and tunability of the magnetoresistance by an electric gate. The large magnetoresistance is due to finite electric field effects at the FM/SC interface, which boost spin-to-charge conversion. The gating scheme we use is based on switching between uni- and bi-directional spin diffusion, without resorting to the spin-orbit coupling.

cond-mat.mtrl-sci↗

arXiv2015

Shot Noise Induced by Nonequilibrium Spin Accumulation

When an electric current passes across a potential barrier, the partition process of electrons at the barrier gives rise to the shot noise, reflecting the discrete nature of the electric charge. Here we report the observation of excess shot noise connected with a spin current which is induced by a nonequilibrium spin accumulation in an all-semiconductor lateral spin-valve device. We find that this excess shot noise is proportional to the spin current. Additionally, we determine quantitatively the spin-injection-induced electron temperature by measuring the current noise. Our experiments show that spin accumulation driven shot noise provides a novel means of investigating nonequilibrium spin transport.

cond-mat.mes-hall↗

arXiv2013

Giant enhancement of spin detection sensitivity in (Ga,Mn)As/GaAs Esaki diodes

We investigate the correlation between spin signals measured in three-terminal (3T) geometry by the Hanle effect and the spin accumulation generated in a semiconductor channel in a lateral (Ga,Mn)As/GaAs Esaki diode device. We systematically compare measurements using a 3T configuration, probing spin accumulation directly beneath the injecting contact, with results from nonlocal measurements, where solely spin accumulation in the GaAs channel is probed. We find that the spin signal detected in the 3T configuration is dominated by a bias-dependent spin detection sensitivity, which in turn is strongly correlated with charge-transport properties of the junction. This results in a particularly strong enhancement of the detected spin signal in a region of increased differential resistance. We find additionally that two-step tunneling via localized states (LS) in the gap of (Ga,Mn)As does not compromise spin injection into the semiconductor conduction band.

cond-mat.mtrl-sci↗

arXiv2013

Annealing-induced magnetic moments detected by spin precession measurements in epitaxial graphene on SiC

We present results of non-local and three terminal (3T) spin precession measurements on spin injection devices fabricated on epitaxial graphene on SiC. The measurements were performed before and after an annealing step at 150 degrees Celsius for 15 minutes in vacuum. The values of spin relaxation length L_s and spin relaxation time tau_s obtained after annealing are reduced by a factor 2 and 4, respectively, compared to those before annealing. An apparent discrepancy between spin diffusion constant D_s and charge diffusion constant D_c can be resolved by investigating the temperature dependence of the g-factor, which is consistent with a model for paramagnetic magnetic moments.

cond-mat.mes-hall↗

arXiv2012

All-electrical measurements of direct spin Hall effect in GaAs with Esaki diode electrodes

We report on measurements of direct spin Hall effect in a lightly n-doped GaAs channel. As spin detecting contacts we employed highly efficient ferromagnetic Fe/(Ga,Mn)As/GaAs Esaki diode structures. We investigate bias and temperature dependence of the measured spin Hall signal and evaluate the value of total spin Hall conductivity and its dependence on channel conductivity and temperature. From the results we determine skew scattering and side jump contribution to the total spin hall conductivity and compare it with the results of experiments on higher conductive n-GaAs channels[Phys. Rev. Lett. 105,156602(2010)]. As a result we conclude that both skewness and side jump contribution cannot be fully independent on the conductivity of the channel.

cond-mat.mes-hall↗

arXiv2012

Nonuniform current density and spin accumulation in a 1 μm thick n-GaAs channel

The spin accumulation in an n-GaAs channel produced by spin extraction into a (Ga,Mn)As contact is measured by cross-sectional imaging of the spin polarization in GaAs. The spin polarization is observed in a 1 \mum thick n-GaAs channel with the maximum polarization near the contact edge opposite to the maximum current density. The one-dimensional model of electron drift and spin diffusion frequently used cannot explain this observation. It also leads to incorrect spin lifetimes from Hanle curves with a strong bias and distance dependence. Numerical simulations based on a two-dimensional drift-diffusion model, however, reproduce the observed spin distribution quite well and lead to realistic spin lifetimes.

cond-mat.mtrl-sci↗

arXiv2010

Local spin valve effect in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

We report on a local spin valve effect observed unambiguously in lateral all-semiconductor all-electrical spin injection devices, employing p+-(Ga,Mn)As/n+-GaAs Esaki diode structures as spin aligning contacts. We discuss the observed local spin-valve signal as a result of interplay between spin-transport-related contribution and tunneling anisotropic magnetoresistance of magnetic contacts. The magnitude of the spin-related magnetoresistance change is equal to 30 Ohm which is twice the magnitude of the measured non-local signal.

cond-mat.mtrl-sci↗

arXiv2009

Tunneling Anisotropic Spin Polarization in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

We report here on anisotropy of spin polarization obtained in lateral all-semiconductor all-electrical spin injection devices, employing $p^{+}-$(Ga,Mn)As/$n^{+}-$GaAs Esaki diode structures as spin aligning contacts, resulting from the dependence of the efficiency of spin tunneling on the orientation of spins with respect to different crystallographic directions. We observed an in-plane anisotropy of $~8%$ in case of spins oriented either along $[1\bar{1}0]$ or $[110]$ directions and $~25%$ anisotropy between in-plane and perpendicular-to-plane orientation of spins.

cond-mat.mtrl-sci↗

arXiv2008

Electrical spin injection and detection in lateral all-semiconductor devices

Electrical injection and detection of spin-polarized electrons is demonstrated for the first time in a single wafer, all-semiconductor, GaAs-based lateral spintronic device, employing p+-(Ga,Mn)As/n+-GaAs ferromagnetic Esaki diodes as spin aligning contacts. The conversion of spin-polarized holes into spin-polarized electrons via Esaki tunnelling leaves its mark in a bias dependence of the spin-injection efficiency, which at maximum reaches the relatively high value of 50%.

cond-mat.mtrl-sci↗