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A. G. M. Jansen

Publications and source records attributed to A. G. M. Jansen.

At least 19 recordsLinked to original sources
arXiv2021

Extreme in-plane upper critical magnetic fields of heavily doped quasi-two-dimensional transition metal dichalcogenides

Extreme in-plane upper critical magnetic fields $B_{c2//ab}$ strongly violating the Pauli paramagnetic limit have been observed in the misfit layer $(LaSe)_{1.14}(NbSe_2)$ and $(LaSe)_{1.14}(NbSe_2)_2$ single crystals with $T_c$ = 1.23 K and 5.7 K, respectively. The crystals show a two-dimensional to three-dimensional transition at temperatures slightly below $T_c$ with an upturn in the temperature dependence of $B_{c2//ab}$, a temperature dependent huge superconducting anisotropy and a cusplike behavior of the angular dependence of $B_{c2}$. Both misfits are characterized by a strong charge transfer from LaSe to $NbSe_2$. As shown in our previous work, $(LaSe)_{1.14}(NbSe_2)$ is electronically equivalent to the highly doped $NbSe_2$ monolayers. Then, the strong upper critical field can be attributed to the Ising coupling recently discovered in atomically thin transition metal dichalcogenides with strong spin-orbit coupling and a lack of inversion symmetry. A very similar behavior is found in $(LaSe)_{1.14}(NbSe_2)_2$, where the charge transfer is nominally twice as big, which could eventually lead to complete filling of the $NbSe_2$ conduction band and opening superconductivity in LaSe. Whatever the particular superconducting mechanism would be, a common denominator in both misfits is that they behave as a stack of almost decoupled superconducting atomic layers, proving that Ising superconductivity can also exist in bulk materials.

cond-mat.supr-con↗
arXiv2021

Compact gate-based read-out of multiplexed quantum devices with a cryogenic CMOS active inductor

In the strive for scalable quantum processors, significant effort is being devoted to the development of cryogenic classical hardware for the control and readout of a growing number of qubits. Here we report on a cryogenic circuit incorporating a CMOS-based active inductor enabling fast impedance measurements with a sensitivity of 10 aF and an input-referred noise of 3.7 aF/sqrt(Hz). This type of circuit is especially conceived for the readout of semiconductor spin qubits. As opposed to commonly used schemes based on dispersive rf reflectometry, which require mm-scale passive inductors, it allows for a markedly reduced footprint (50$μ$m $\times$ 60$μ$m), facilitating its integration in a scalable quantum-classical architecture. In addition, its active inductor results in a resonant circuit with tunable frequency and quality factor, enabling the optimization of readout sensitivity.

quant-ph↗
arXiv2019

Cryogenic characterization of 28nm FD-SOI ring oscillators with energy efficiency optimization

Extensive electrical characterization of ring oscillators (ROs) made in high-$κ$ metal gate 28nm Fully-Depleted Silicon-on- Insulator (FD-SOI) technology is presented for a set of temperatures between 296 and 4.3K. First, delay per stage ($τ_P$), static current ($I_{STAT}$), and dynamic current ($I_{DYN}$) are analyzed for the case of the increase of threshold voltage ($V_{TH}$) observed at low temperature. Then, the same analysis is performed by compensating $V_{TH}$ to a constant, temperature independent value through forward body-biasing (FBB). Energy efficiency optimization is proposed for different supply voltages ($V_{DD}$) in order to find an optimal operating point combining both high RO frequencies and low power dissipation. We show that the Energy-Delay product ($EDP$) can be significantly reduced at low temperature by applying a forward body bias voltage ($V_{FBB}$). We demonstrate that outstanding performance of RO in terms of speed ($τ_P$=37ps) and static power (7nA/stage) can be achieved at 4.3K with $V_{DD}$ reduced down to 0.325V.

physics.app-ph↗
arXiv2019

Cryogenic Subthreshold Swing Saturation in FD-SOI MOSFETs described with Band Broadening

In the standard MOSFET description of the drain current $I_{D}$ as a function of applied gate voltage $V_{GS}$, the subthreshold swing $SS(T)\equiv dV_{GS}/d\log I_{D}$ has a fundamental lower limit as a function of temperature $T$ given by $SS(T) = \ln10~k_BT/e$. However, recent low-temperature studies of different advanced CMOS technologies have reported $SS$(4K or lower) values that are at least an order of magnitude larger. Here, we present and analyze the saturation of $SS(T)$ in 28nm fully-depleted silicon-on-insulator (FD-SOI) devices for both n- and p-type MOSFETs of different gate oxide thicknesses and gate lengths down to 4K. Until now, the increase of interface-trap density close to the band edge as temperature decreases has been put forward to understand the saturation. Here, an original explanation of the phenomenon is presented by considering a disorder-induced tail in the density of states at the conduction (valence) band edge for the calculation of the MOS channel transport by applying Fermi-Dirac statistics. This results in a subthreshold $I_{D}\sim e^{eV_{GS}/k_BT_0}$ for $T_0=35$K with saturation value $SS(T<T_0) = \ln 10~k_BT_0/e$. The proposed model adequately describes the experimental data of $SS(T)$ from 300 down to 4K using $k_BT_0 \simeq 3$meV for the width of the exponential tail and can also accurately describe $SS(I_{D})$ within the whole subthreshold region. Our analysis allows a direct determination of the technology-dependent band-tail extension forming a crucial element in future compact modeling and design of cryogenic circuits.

cond-mat.mes-hall↗
arXiv2018

Electronic spectrum of twisted graphene layers under heterostrain

We demonstrate that stacking layered materials allows a novel type of strain engineering where each layer is strained independently, which we call heterostrain. We combine detailed structural and spectroscopic measurements with tight-binding calculations to show that small uniaxial heterostrain suppresses Dirac cones and leads to the emergence of flat bands in twisted graphene layers (TGLs). Moreover, we demonstrate that heterostrain reconstructs much more severely the energy spectrum of TGLs than homostrain for which both layers are strained identically ; a result which should apply to virtually all van der Waals structure opening exciting possibilities for straintronics with 2D materials.

cond-mat.mes-hall↗
arXiv2017

Influence of nonequilibrium phonons on the amplitude of magnetoquantum oscillations in the point-contact resistance

For metallic point contacts with Be and Al the magnetoquantum oscillations in the contact resistance have been investigated as a function of the applied voltage over the contact. For one set of point contacts the oscillation amplitude is found to vary nonmonotonously with the applied voltage with similarities to the point-contact spectrum of the electron-phonon interaction. The other part of the investigated point contacts shows a decrease of the oscillation amplitude with increasing bias voltage. For the understanding of the voltage dependence of the amplitude of the point-contact magnetoresistance oscillations the influence of nonequilibrium phonons generated by the ballistically injected electrons will be discussed.

cond-mat.mes-hall↗
arXiv2017

Tunneling measurements of the electron-phonon interaction in $\rm Ba_{1-x}K_xBiO_3$

The conductance curves of point-contact tunnel junctions between Ag and $\rm Ba_{1-x}K_xBiO_3$ ($x\simeq 0.4$) reveal a BCS behavior with low leakage current at zero voltage and some broadening of the superconducting-gap structure. In the energy range above the superconducting energy gap, the structure in the voltage dependence of the second derivative $d^2V/dI^2$ of the voltage with respect to the current of the tunnel junction has been investigated in detail in magnetic fields up to $10\ T$. While part of this structure is rapidly changing in a magnetic field, three reproducible peaks in $d^2V/dI^2(V)$ remain stable up to the transition temperature from the superconducting to the normal state with only additional broadening in the applied magnetic field. An analysis of this structure in terms of strong-coupling effects yields the spectral function $α^2F$ for the electron-phonon interaction. The obtained spectral weight in the energy region 20-70~$meV$ points to the importance of the oxygen optical modes in the electron-phonon coupling for the superconductivity of $\rm Ba_{1-x}K_xBiO_3$.

cond-mat.supr-con↗
arXiv2017

Reversible transitions in high-$T_c$ cuprates based point contacts

The influence of electric felds and currents has been investigated in the high-$T_c$ superconductors $YBaCuO$ and $BiSrCaCuO$ using a point-contact geometry with $Ag$ as the counterelectrode, which reveal switching transitions between states of a different resistance. The origin of this effect in point contacts is associated with electromigration of the oxygen, driven by the electric feld as well as by the currentinduced "electron wind". The switching effect preserves its basic features at elevated temperatures up to room temperature and in high magnetic felds up to 10 T.

cond-mat.supr-con↗
arXiv2016

Magnetoquantum oscillations in the resistance of metallic point contacts: Influence of nonequilibrium phonons

The amplitude of magnetoresistance quantum oscillations of Al and Be point contacts in a magnetic field parallel to the contact axis has been studied as a function of voltage applied over the contact. It was found that for one group of contacts the oscillation amplitude nonmonotonously increases with the bias voltage increase, while for the other part of the contacts a decrease of amplitude was observed. The scattering of electrons with nonequilibrium phonons and also phonon-phonon collisions will be discussed as the possible reasons of the observed effects.

cond-mat.mes-hall↗
arXiv2013

Thermoelectric effects and the asymmetry of the current-voltage characteristics of metallic point contacts

An asymmetry as a function of the direction of current flow is observed in the current-voltage characteristic (CVC) and its first and second derivatives for point heterocontacts between pure metals {Cu, Ni, Fe) as well as between these metals and dilute alloys (CuFe, CuMn). It is shown that the observed asymmetry is caused by thermoelectrical phenomena (Seebeck, Peltier, and Thompson effects), observed when the temperature inside the contact differs from the temperature of the bath. In the low energy range (less than or of the order of the Debye energy) the asymmetry of the CVC is affected mainly by the Seebeck effect, while at high energies and for larger contacts (lower resistance) the contributions of all noted effects are of the same order of magnitude. A technique is proposed for determining the temperature of a heterocontact by measuring the CVC in two polarities. It is established that in the intermediate (between the diffusion and ballistic) state of flight of the electrons through the constriction the temperature of the heterocontact increases linearly with the voltage on it, and all the more rapidly the larger the contact and the more impurity in it.

cond-mat.mes-hall↗
arXiv2010

Condon Domain Phase Diagram and Hysteresis Size for Beryllium

The Condon domain phase diagram for beryllium is determined in magnetic fields up to 10 T and at temperatures down to 1.3 K using a standard ac pick-up coil method to measure the de Haas-van Alphen (dHvA) effect. The detection of the transition point from the homogeneous state to the Condon domain state (CDS) is based on the extremely non-linear response to the modulation field resulting from a small irreversibility in the dHvA magnetization. The experimental results are compared with theoretical predictions calculated from the Fermi surface (FS) of beryllium. The width h_m of the hysteresis loop in the CDS is measured in a wide temperature and field region. A model for the hysteresis size is proposed and numerically calculated for the whole phase diagram.

cond-mat.str-el↗
arXiv2010

Condon Domain Phase Diagram for Silver

We present the Condon domain phase diagram for a silver single crystal measured in magnetic fields up to 28 T and temperatures down to 1.3 K. A standard ac method with a pickup coil system is used at low frequency for the measurements of the de Haas-van Alphen effect (dHvA). The transition point from the state of homogeneous magnetization to the inhomogeneous Condon domain state (CDS) is found as the point where a small irreversibility in the dHvA magnetization arises, as manifested by an extremely nonlinear response in the pickup voltage showing threshold character. The third harmonic content in the ac response is used to determine with high precision the CDS phase boundary. The experimentally determined Condon domain phase diagram is in good agreement with the theoretical prediction calculated by the standard Lifshitz-Kosevich (LK) formula.

cond-mat.str-el↗
arXiv2009

Suppression of asymmetric differential resistance in non-Fermi liquid system YbCu_(5-x)Al_(x) (x = 1.3 - 1.75) in high magnetic fields

The non-Fermi liquid system (NFL) YbCu_(5-x)Al_(x) (x = 1.3 - 1.75) has been investigated in hetero- as well as homo-contact arrangement in magnetic fields up to 22.5 T. The observed dV/dI(V) characteristics reveal asymmetry in hetero-contact arrangement and do not agree with the model of thermal contact heating, at least close to zero-bias voltage. In the case of a hetero-contact arrangement we have observed a maximum at only one voltage polarity at about 1.3 mV (for x = 1.5), which asymmetry is suppressed in an applied magnetic field. This behavior is connected with NFL properties of studied compounds.

cond-mat.str-el↗
arXiv2006

Scaling flow diagram in the fractional quantum Hall regime of GaAs/AlGaAs heterostructures

The temperature driven flow lines of the Hall and dissipative magnetoconductance data (σ_{xy},σ_{xx}) are studied in the fractional quantum Hall regime for a 2D electron system in GaAs/Al_{x}Ga_{1-x}As heterostructures. The flow lines are rather well described by a recent unified scaling theory developed for both the integer and the fractional quantum Hall effect in a totally spin-polarized 2D electron system which predicts that one (σ_{xy},σ_{xx}) point determines a complete flow line.

cond-mat.mes-hall↗
arXiv2005

Hysteresis in the de Haas-van Alphen Effect

A hysteresis loop is observed for the first time in the de Haas-van Alphen (dHvA) effect of beryllium at low temperatures and quantizing magnetic field applied parallel to the hexagonal axis of the single crystal. The irreversible behavior of the magnetization occurs at the paramagnetic part of the dHvA period in conditions of Condon domain formation arising by strong enough dHvA amplitude. The resulting extremely nonlinear response to a very small modulation field offers the possibility to find in a simple way the Condon domain phase diagram. From a harmonic analysis, the shape and size of the hysteresis loop is constructed.

cond-mat.mtrl-sci↗
arXiv2005

Direct Observation of Condon Domains in Silver by Hall Probes

Using a set of micro Hall probes for the detection of the local induction, the inhomogeneous Condon domain structure has been directly observed at the surface of a pure silver single crystal under strong Landau quantization in magnetic fields up to 10 T. The inhomogeneous induction occurs in the theoretically predicted part of the H-T Condon domain phase diagram. Information about size, shape and orientation of the domains is obtained by analyzing Hall probes placed along and across the long sample axis and by tilting the sample. On a beryllium surface the induction inhomogeneity is almost absent although the expected induction splitting here is at least ten times higher than in silver.

cond-mat.mtrl-sci↗
arXiv2005

Deviations from plastic barriers in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ thin films

Resistive transitions of an epitaxial Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ thin film were measured in various magnetic fields ($H\parallel c$), ranging from 0 to 22.0 T. Rounded curvatures of low resistivity tails are observed in Arrhenius plot and considered to relate to deviations from plastic barriers. In order to characterize these deviations, an empirical barrier form is developed, which is found to be in good agreement with experimental data and coincide with the plastic barrier form in a limited magnetic field range. Using the plastic barrier predictions and the empirical barrier form, we successfully explain the observed deviations.

cond-mat.supr-con↗