The war in Ukraine is still going on. The number of victims is increasing every day. Many researc... more The war in Ukraine is still going on. The number of victims is increasing every day. Many research centers are destroyed, researchers are displaced, and the conditions and nature of work in almost all regions of Ukraine have undergone significant changes. Is it time to talk about the future of physics in Ukraine under such conditions now? It is our deep conviction that it is necessary.
Fermi surfaces are essential for predicting, characterizing and controlling the properties of cry... more Fermi surfaces are essential for predicting, characterizing and controlling the properties of crystalline metals and semiconductors. Angle-resolved photoemission spectroscopy (ARPES) is the only technique directly probing the Fermi surface by measuring the Fermi momenta (kF) from energy- and angular distribution of photoelectrons dislodged by monochromatic light. Existing apparatus is able to determine a number of kF -vectors simultaneously, but direct high-resolution 3D Fermi surface mapping remains problematic. As a result, no such datasets exist, strongly limiting our knowledge about the Fermi surfaces. Here we show that using a simpler instrumentation it is possible to perform 3D-mapping within a very short time interval and with very high resolution. We present the first detailed experimental 3D Fermi surface as well as other experimental results featuring advantages of our technique. In combination with various light sources our methodology and instrumentation offer new opport...
2021 IEEE 12th International Conference on Electronics and Information Technologies (ELIT)
Superconducting qubits demonstrate good perspectives as scalable blocks for quantum information p... more Superconducting qubits demonstrate good perspectives as scalable blocks for quantum information processing. These systems can be individually readout, addressed, and controlled, making them some of the most attractive thin-film qubits. Quantum measurements should be performed in order to readout the final state of flux qubits. To observe the dynamics of such systems, one requires a fast magnetometer with exceptional sensitivity and low back-action. We address the problem of reducing the back-action of an RF SQUID readout circuit, which may significantly destroy a Josephson flux qubit in the case of the circuits integration. The main sources of such back-action in conventional RF SQUID and DC SQUID circuits are low-ohmic shunting resistors ensuring high damping. The advantage of flux qubits is the presence of an optimal bias point at which, in the first-order approximation, the device is immune to fluctuations in readout and control lines. Nonetheless, even such systems have characteristics limited by a second-order dissipation. The dissipation can be eliminated by using an “ideal parametric readout” based on an RF SQUID acting in non-hysteretic adiabatic mode. In this paper, we propose an RF SQUID in a non-hysteretic regime as a fast, sensitive, and scalable readout system with low back-action for measurements of a single MW photon counter based on a flux qubit.
Origin of the peak-dip-hump structure in the photoemission spectra of Bi 2Sr 2CaCu 2O 8 The scien... more Origin of the peak-dip-hump structure in the photoemission spectra of Bi 2Sr 2CaCu 2O 8 The scientific and technological significance of high temperature superconductivity (HTSC) has made cuprates perhaps the most studied objects in the history of condensed matter physics. Unlike their conventional counterparts for which the theory is well developed, the cuprate superconductors still guard their secret despite extensive efforts undertaken by the scientific community during the last 15 years. The central question is: what helps the electrons to co-operate at low temperatures to carry the superconducting current? It is known that in the case of simple metals formation of electron pairs is driven by the coupling between electrons and phonons. In the high Tc cuprates, the nature of the force driving the pairing is of yet unknown or controversial origin. A wealth of information related to this issue has been provided by angle-resolved photoemission spectroscopy (ARPES), which has emerged...
Mass renormalization of the charge carriers in high-T c superconductors Superconductivity in conv... more Mass renormalization of the charge carriers in high-T c superconductors Superconductivity in conventional superconductors such as Pb or Nb is explained by a formation of pairs of the charge carriers due to a coupling to lattice vibrations. In the cuprate high-Tc superconductors the formation of singlet pairs of charge carriers has been demonstrated but the glue for the formation of pairs is not known. As a consequence, there is a consensus that there is at present no consensus on the microscopic theory for high-Tc superconductivity. Using angle-resolved photoemission spectroscopy with unprecedented precision we have detected a very strong coupling of the charge carriers below Tc to a bosonic mode with an energy of 40 meV. From the temperature and dopant dependence we conclude that this mode is related to spin fluctuations thus favoring an electronic mechanism for high-Tc superconductivity. Fig.1: Highest superconducting
Experimental studies of the electronic structure remain the basic means for understanding the nat... more Experimental studies of the electronic structure remain the basic means for understanding the nature of high-temperature superconductivity (HTSC) and testing relevant theoretical models. Appreciable contributions to establish the overall picture in HTSC have recently been made by investigations on the charge dynamics in BSCCO (ref. 1) and the spin dynamics in YBCO, using Angle Resolved Photoemission Spectroscopy (ARPES) and Inelastic Neutron Scattering (INS), respectively. Concentration of each of these techniques on a "suitable" compound turns out to be a barrier on the way to a crucial quantitative test allowing to support or discard spin fluctuations (interaction between the charge and spin degrees of freedom) as a possible origin for the pairing in doped cuprates. Here we solve the long-standing puzzle of ARPES on YBCO by showing that the photoelectron spectrum of YBCO generally includes two components: One from the topmost anomalously overdoped metallic CuO2 bilayer a...
We present a novel mechanism of resistive-switching phenomenon in nanoscale point-contact devices... more We present a novel mechanism of resistive-switching phenomenon in nanoscale point-contact devices based on conducting perovskites, cuprates, manganites, and bismuthates. The measurements of their current-voltage characteristics at room temperature and 77 K have revealed bipolar hysteretic behavior that is caused, in our opinion, by the presence of a ferroelectric phase in the near-interface region of the complex-oxide samples. We interpret our observations in terms of the active oxygen-deficient layer formed at the metal-perovskite oxide interface where the electric-dipole moment switching is induced by an external electric field.
The war in Ukraine is still going on. The number of victims is increasing every day. Many researc... more The war in Ukraine is still going on. The number of victims is increasing every day. Many research centers are destroyed, researchers are displaced, and the conditions and nature of work in almost all regions of Ukraine have undergone significant changes. Is it time to talk about the future of physics in Ukraine under such conditions now? It is our deep conviction that it is necessary.
Fermi surfaces are essential for predicting, characterizing and controlling the properties of cry... more Fermi surfaces are essential for predicting, characterizing and controlling the properties of crystalline metals and semiconductors. Angle-resolved photoemission spectroscopy (ARPES) is the only technique directly probing the Fermi surface by measuring the Fermi momenta (kF) from energy- and angular distribution of photoelectrons dislodged by monochromatic light. Existing apparatus is able to determine a number of kF -vectors simultaneously, but direct high-resolution 3D Fermi surface mapping remains problematic. As a result, no such datasets exist, strongly limiting our knowledge about the Fermi surfaces. Here we show that using a simpler instrumentation it is possible to perform 3D-mapping within a very short time interval and with very high resolution. We present the first detailed experimental 3D Fermi surface as well as other experimental results featuring advantages of our technique. In combination with various light sources our methodology and instrumentation offer new opport...
2021 IEEE 12th International Conference on Electronics and Information Technologies (ELIT)
Superconducting qubits demonstrate good perspectives as scalable blocks for quantum information p... more Superconducting qubits demonstrate good perspectives as scalable blocks for quantum information processing. These systems can be individually readout, addressed, and controlled, making them some of the most attractive thin-film qubits. Quantum measurements should be performed in order to readout the final state of flux qubits. To observe the dynamics of such systems, one requires a fast magnetometer with exceptional sensitivity and low back-action. We address the problem of reducing the back-action of an RF SQUID readout circuit, which may significantly destroy a Josephson flux qubit in the case of the circuits integration. The main sources of such back-action in conventional RF SQUID and DC SQUID circuits are low-ohmic shunting resistors ensuring high damping. The advantage of flux qubits is the presence of an optimal bias point at which, in the first-order approximation, the device is immune to fluctuations in readout and control lines. Nonetheless, even such systems have characteristics limited by a second-order dissipation. The dissipation can be eliminated by using an “ideal parametric readout” based on an RF SQUID acting in non-hysteretic adiabatic mode. In this paper, we propose an RF SQUID in a non-hysteretic regime as a fast, sensitive, and scalable readout system with low back-action for measurements of a single MW photon counter based on a flux qubit.
Origin of the peak-dip-hump structure in the photoemission spectra of Bi 2Sr 2CaCu 2O 8 The scien... more Origin of the peak-dip-hump structure in the photoemission spectra of Bi 2Sr 2CaCu 2O 8 The scientific and technological significance of high temperature superconductivity (HTSC) has made cuprates perhaps the most studied objects in the history of condensed matter physics. Unlike their conventional counterparts for which the theory is well developed, the cuprate superconductors still guard their secret despite extensive efforts undertaken by the scientific community during the last 15 years. The central question is: what helps the electrons to co-operate at low temperatures to carry the superconducting current? It is known that in the case of simple metals formation of electron pairs is driven by the coupling between electrons and phonons. In the high Tc cuprates, the nature of the force driving the pairing is of yet unknown or controversial origin. A wealth of information related to this issue has been provided by angle-resolved photoemission spectroscopy (ARPES), which has emerged...
Mass renormalization of the charge carriers in high-T c superconductors Superconductivity in conv... more Mass renormalization of the charge carriers in high-T c superconductors Superconductivity in conventional superconductors such as Pb or Nb is explained by a formation of pairs of the charge carriers due to a coupling to lattice vibrations. In the cuprate high-Tc superconductors the formation of singlet pairs of charge carriers has been demonstrated but the glue for the formation of pairs is not known. As a consequence, there is a consensus that there is at present no consensus on the microscopic theory for high-Tc superconductivity. Using angle-resolved photoemission spectroscopy with unprecedented precision we have detected a very strong coupling of the charge carriers below Tc to a bosonic mode with an energy of 40 meV. From the temperature and dopant dependence we conclude that this mode is related to spin fluctuations thus favoring an electronic mechanism for high-Tc superconductivity. Fig.1: Highest superconducting
Experimental studies of the electronic structure remain the basic means for understanding the nat... more Experimental studies of the electronic structure remain the basic means for understanding the nature of high-temperature superconductivity (HTSC) and testing relevant theoretical models. Appreciable contributions to establish the overall picture in HTSC have recently been made by investigations on the charge dynamics in BSCCO (ref. 1) and the spin dynamics in YBCO, using Angle Resolved Photoemission Spectroscopy (ARPES) and Inelastic Neutron Scattering (INS), respectively. Concentration of each of these techniques on a "suitable" compound turns out to be a barrier on the way to a crucial quantitative test allowing to support or discard spin fluctuations (interaction between the charge and spin degrees of freedom) as a possible origin for the pairing in doped cuprates. Here we solve the long-standing puzzle of ARPES on YBCO by showing that the photoelectron spectrum of YBCO generally includes two components: One from the topmost anomalously overdoped metallic CuO2 bilayer a...
We present a novel mechanism of resistive-switching phenomenon in nanoscale point-contact devices... more We present a novel mechanism of resistive-switching phenomenon in nanoscale point-contact devices based on conducting perovskites, cuprates, manganites, and bismuthates. The measurements of their current-voltage characteristics at room temperature and 77 K have revealed bipolar hysteretic behavior that is caused, in our opinion, by the presence of a ferroelectric phase in the near-interface region of the complex-oxide samples. We interpret our observations in terms of the active oxygen-deficient layer formed at the metal-perovskite oxide interface where the electric-dipole moment switching is induced by an external electric field.
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