arXiv subjects

Yoram Dagan

Publications and source records attributed to Yoram Dagan.

12 recordsLinked to original sources

arXiv2025

Freestanding single-crystal superconducting electron-doped cuprate membrane

Thin films of cuprate superconductors are easier to control in terms of doping as compared to bulk samples. However, they require specific substrates to facilitate epitaxial growth. These substrates are often incompatible with materials used in electronic applications. Furthermore, it is challenging to separate the substrate's properties from the material of interest. Here, we demonstrate the fabrication of an electron-doped cuprate membrane. We show that the membrane has a coherent crystal structure. Furthermore, the superconducting properties of the membrane post-liftoff closely resemble those of the thin films pre-lift-off, as revealed by a scanning superconducting quantum interference device (SQUID) microscope. Such membranes pave the way for designing new material properties and incorporating complex superconducting materials into typically incompatible electronic devices.

cond-mat.supr-con↗

arXiv2024

Charge gain via solid-state gating of an oxide Mott system

The modulation of channel conductance in field-effect transistors (FETs) via metal-oxide-semiconductor (MOS) structures has revolutionized information processing and storage. However, the limitations of silicon-based FETs in electrical switching have driven the search for new materials capable of overcoming these constraints. Electrostatic gating of competing electronic phases in a Mott material near its metal to insulator transition (MIT) offers prospects of substantial modulation of the free carriers and electrical resistivity through small changes in band filling. While electrostatic control of the MIT has been previously reported, the advancement of Mott materials towards novel Mott transistors requires the realization of their charge gain prospects in a solid-state device. In this study, we present gate-control of electron correlation using a solid-state device utilizing the oxide Mott system $La_{1-x}Sr_xVO_3$ as a correlated FET channel. We report on a gate resistance response that cannot be explained in a purely electrostatic framework, suggesting at least $\times100$ charge gain originating from the correlated behavior. These preliminary results pave the way towards the development of highly efficient, low-power electronic devices that could surpass the performance bottlenecks of conventional FETs by leveraging the electronic phase transitions of correlated electron systems.

cond-mat.str-el↗

arXiv2022

Tunable Magnetic Scattering and Ferroelectric Switching at the LaAlO$_3$/EuTiO$_3$/Sr$_{0.99}$Ca$_{0.01}$TiO$_3$ Interface

Ferroelectric and ferromagnetic orders rarely coexist, and magnetoelectric coupling is even more scarce. A possible avenue for combining these orders is by interface design, where orders formed at the constituent materials can overlap and interact. Using a combination of magneto-transport and scanning SQUID measurements, we explore the interactions between ferroelectricity, magnetism, and the 2D electron system (2DES) formed at the novel LaAlO$_3$/EuTiO$_3$/Sr$_{0.99}$Ca$_{0.01}$TiO$_3$ heterostructure. We find that the electrons at the interface experience magnetic scattering appearing along with a diverging Curie-Weiss-type behaviour in the EuTiO$_3$ layer. The 2DES is also affected by the switchable ferroelectric polarization at the Sr$_{0.99}$Ca$_{0.01}$TiO$_3$ bulk. While the 2DES interacts with both magnetism and ferroelectricity, we show that the presence of the conducting electrons has no effect on magnetization in the EuTiO$_3$ layer. Our results provide a first step towards realizing a new multiferroic system where magnetism and ferroelectricity can interact via an intermediate conducting layer.

cond-mat.str-el↗

arXiv2020

Ferroelectric Exchange Bias Affects Interfacial Electronic States

In polar oxide interfaces phenomena such as conductivity, superconductivity, magnetism, one-dimensional conductivity and Quantum Hall states can emerge at the polar discontinuity. Combining controllable ferroelectricity at such interfaces can affect the superconducting properties and shed light on the mutual effects between the polar oxide and the ferroelectric oxide. Here we study the interface between the polar oxide LaAlO3 and the ferroelectric Ca-doped SrTiO3 by means of electrical transport combined with local imaging of the current flow with the use of scanning Superconducting Quantum Interference Device (SQUID). Anomalous behavior of the interface resistivity is observed at low temperatures. The scanning SQUID maps of the current flow suggest that this behavior originates from an intrinsic bias induced by the polar LaAlO3 layer. Our data imply that the intrinsic bias combined with ferroelectricity constrain the possible structural domain tiling near the interface. We recommend the use of this intrinsic bias as a method of controlling and tuning the initial state of ferroelectric materials by design of the polar structure. The hysteretic dependence of the normal and the superconducting state properties on gate voltage can be utilized in multifaceted controllable memory devices.

cond-mat.str-el↗

arXiv2019

Symmetry and correlation effects on band structure explain the anomalous transport properties of (111) LaAlO$_3$/SrTiO$_3$

The interface between the two insulating oxides SrTiO$_3$ and LaAlO$_3$ gives rise to a two-dimensional electron system with intriguing transport phenomena, including superconductivity, which are controllable by a gate. Previous measurements on the (001) interface have shown that the superconducting critical temperature, the Hall density, and the frequency of quantum oscillations, vary nonmonotonically and in a correlated fashion with the gate voltage. In this paper we experimentally demonstrate that the (111) interface features a qualitatively distinct behavior, in which the frequency of Shubnikov-de Haas oscillations changes monotonically, while the variation of other properties is nonmonotonic albeit uncorrelated. We develop a theoretical model, incorporating the different symmetries of these interfaces as well as electronic-correlation-induced band competition. We show that the latter dominates at (001), leading to similar nonmonotonicity in all observables, while the former is more important at (111), giving rise to highly curved Fermi contours, and accounting for all its anomalous transport measurements.

cond-mat.str-el↗

arXiv2017

Superconductor-insulator transition in fcc-GeSb2Te4 at elevated pressures

We show that polycrystalline GeSb2Te4 in the fcc phase (f-GST), which is an insulator at low temperature at ambient pressure, becomes a superconductor at elevated pressures. Our study of the superconductor to insulator transition versus pressure at low temperatures reveals a second order quantum phase transition with linear scaling (critical exponent close to unity) of the transition temperature with the pressure above the critical zero-temperature pressure. In addition, we demonstrate that at higher pressures the f-GST goes through a structural phase transition via amorphization to bcc GST (b-GST), which also become superconducting. We also find that the pressure regime where an inhomogeneous mixture of amorphous and b-GST exists, there is an anomalous peak in magnetoresistance, and suggest an explanation for this anomaly.

cond-mat.supr-con↗

arXiv2017

Correlation-Induced Band Competition in SrTiO3/LaAlO3

The oxide interface SrTiO3/LaAlO3 supports a 2D electron liquid displaying superconductivity and magnetism, while allowing for a continuous control of the electron density using a gate. Our recent measurements have shown a similar surprising nonmonotonic behavior as function of the gate voltage (carrier density) of three quantities: the superconducting critical temperature and field, the inverse Hall coefficient, and the frequency of quantum oscillations. While the total density has to be monotonic as function of gate, the last result indicates that one of the involved bands has a nonmontonic occupancy as function of the chemical potential. We show how electronic interactions can lead to such an effect, by creating a competition between the involved bands and making their structure non-rigid, and thus account for all these effects. Adding Fock terms to our previous Hartree treatment makes this scenario even more generic.

cond-mat.str-el↗

arXiv2016

Fermi Surface Reconstruction in the Electron-doped Cuprate Pr(2-x)CexCuO4

We report extensive resistivity, Hall, and magnetoresistance measurements on thin films of the electron-doped cuprate \PCCO~(PCCO), as a function of doping, temperature and magnetic field. The doping dependence of the resistivity and Hall number at low temperatures are characteristic of a system near a quantum phase transition or a Fermi Surface Reconstruction (FSR) point. The spin magnetoresistance drops to zero near the critical point. The data presented in this paper were compiled during the 2004-2007 period but were never published in this comprehensive form. Because of the recent interest in very similar results now being found in the normal state of hole-doped cuprates, we believe the results of our older, mostly unpublished, work will be of interest to the present community of cuprate researchers. In particular, Fig.11 shows the large change in Hall number at the FSR point in \PCCO, similar to that found recently in YBCO and LSCO (See ref[1] and [2]). Also, Fig.6 illustrates how the resistivity upturn is affected by the FSR. The cause of the resistivity upturn has been attributed to the loss of carriers at doping below the FSR in the hole-doped cuprates (see Ref. 3), however, this scenario does not explain the data for PCCO. The upturn in n-doped cuprates is more-likely due to a combination of carrier decrease and a change in the scattering rate below the FSR (see also Ref. 4). The change in spin scattering below the FSR is illustrated by Fig.18 in this paper. Chen et al. [5] have developed a model based on spin scattering that is able to explain qualitatively the resistivity upturn in all the cuprates.

cond-mat.supr-con↗

arXiv2014

Onset of Nernst Effect Beyond the Coherence Critical Field of a Nano-Scale Granular Superconductor

We report measurements of the Nernst effect and of the magneto-resistance of granular aluminum films near the metal to insulator transition. These films show sharp transitions as a function of temperature and magnetic field. At low temperatures the Nernst signal displays a sharp peak at a field where more than 90% of the normal state resistance has been restored, suggesting a transition involving entropy transport after superconducting coherence has been destroyed. At temperatures higher than the critical temperature the fluctuation paraconductivity scales with the Nernst signal, in agreement with a description in terms of fluctuations of the order parameter.

cond-mat.supr-con↗

arXiv2013

Anomalous response to gate voltage application in mesoscopic LaAlO_3/SrTiO_3 devices

We report on resistivity and Hall measurements performed on a series of narrow mesa devices fabricated from LaAlO_3/SrTiO_3 single interface heterostructure with a bridge width range of 1.5-10 microns. Upon applying back-gate voltage of the order of a few Volts, a strong increase in the sample resistance (up to factor of 35) is observed, suggesting a relatively large capacitance between the Hall-bar and the gate. The high value of this capacitance is due to the device geometry, and can be explained within an electrostatic model using the Thomas Fermi approximation. The Hall coefficient is sometimes a non-monotonic function of the gate voltage. This behavior is inconsistent with a single conduction band model. We show that a theoretical two-band model is consistent with this transport behavior, and indicates a metal to insulator transition in at least one of these bands.

cond-mat.mes-hall↗

arXiv2011

Evolution of a bosonic mode across the superconducting dome in the high-Tc cuprate Pr(2-x)Ce(x)CuO(4-δ)

We report a detailed spectroscopic study of the electron doped cuprate superconductor Pr(2-x)Ce(x)CuO(4-δ) using point contact junctions for x=0.125(underdoped), x=0.15(optimally doped) and x=0.17(overdoped). From our conductance measurements we are able to identify bosonic resonances for each doping. These excitations disappear above the critical temperature, and above the critical magnetic field. We find that the energy of the bosonic excitations decreases with doping, which excludes lattice vibrations as the paring glue. We conclude that the bosonic mediator for these cuprates is more likely to be spin excitations.

cond-mat.supr-con↗

arXiv2001

Origin of time reversal symmetry breaking in Y(1-y)Ca(y)Ba(2)Cu(3)O(7-x)

We have studied the Zero Bias Conductance Peak (ZBCP) of the tunneling conductance measured on (1,1,0) oriented Y(1-y)Ca(y)Ba(2)Cu(3)O(7-x) thin films as a function of doping and of magnetic field. A spontaneous (zero field) split of the ZBCP was observed only in overdoped samples (either by O or by Ca). The magnitude of this split was found to be linear in doping. All samples exhibited a magnetic field splitting, also strongly doping dependent. The field susceptibility chi=d(delta)/dH diverges at the point at which spontaneous ZBCP splitting occurs, its inverse value, chi^(-1), following a linear doping dependence on both the underdoped and overdoped sides. We discuss these results in terms of recent theoretical models of Time Reversal Symmetry Breaking (TRSB).

cond-mat.supr-con↗