### Browsing by Author "Golubev, Dmitry"

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Item Andreev current for low temperature thermometry(2015) Faivre, T.; Golubev, Dmitry; Pekola, Jukka; Department of Applied PhysicsWe demonstrate experimentally that disorder enhanced Andreev current in a tunnel junction between a normal metal and a superconductor provides a method to measure electronic temperature, specifically at temperatures below 200 mK when aluminum is used. This Andreev thermometer has some advantages over conventional quasiparticle thermometers: For instance, it does not conduct heat and its reading does not saturate until at lower temperatures. Another merit is that the responsivity is constant over a wide temperature range.Item Exactly solvable model of calorimetric measurements(American Physical Society, 2020-12-01) Donvil, Brecht; Muratore-Ginanneschi, Paolo; Golubev, Dmitry; University of Helsinki; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsCalorimetric measurements are experimentally realizable methods to assess thermodynamics relations in quantum devices. With this motivation in mind, we consider a resonant level coupled to a Fermion reservoir. We consider a transient process in which the interaction between the level and the reservoir is initially switched on and then switched off again. We find the time dependence of the energy of the reservoir, of the energy of the level, and of the interaction energy between them at weak, intermediate, strong, and ultrastrong coupling. We also determine the statistical distributions of these energies.Item Heat switch and thermoelectric effects based on Cooper-pair splitting and elastic cotunneling(American Physical Society, 2019-03-18) Kirsanov, N. S.; Tan, Zhenbing; Golubev, Dmitry; Hakonen, Pertti J.; Lesovik, Gordey; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Quantum Circuits and CorrelationsIn this paper, we demonstrate that the hybrid normal-superconducting-normal (NSN) structure has potential for a multifunctional thermal device which could serve for heat flux control and cooling of microstructures. By adopting the scattering matrix approach, we theoretically investigate thermal and electrical effects emerging in such structures due to the Cooper pair splitting (CPS) and elastic cotunneling phenomena. We show that a finite superconductor can, in principle, mediate heat flow between normal leads, and we further clarify special cases when this seems contradictory to the second law of thermodynamics. Among other things, we demonstrate that the CPS phenomenon can appear even in the simple case of a ballistic NSN structure.Item Heat transport through a Josephson junction(American Physical Society (APS), 2013) Golubev, Dmitry; Faivre, Timothé; Pekola, Jukka P.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe discuss heat transport through a Josephson tunnel junction under various bias conditions. We first derive the formula for the cooling power of the junction valid for arbitrary time dependence of the Josephson phase. Combining it with the classical equation of motion for the phase, we find the time-averaged cooling power as a function of bias current or bias voltage. We also find the noise of the heat current and, more generally, the full counting statistics of the heat transport through the junction. We separately consider the metastable superconducting branch of the current-voltage characteristics allowing quantum fluctuations of the phase in this case. This regime is experimentally attractive since the junction has low power dissipation, low impedance, and therefore may be used as a sensitive detector.Item Heat transport through a Josephson junction(2013-03-29) Golubev, Dmitry; Faivre, Timothe; Pekola, Jukka P.; Department of Applied PhysicsWe discuss heat transport through a Josephson tunnel junction under various bias conditions. We first derive the formula for the cooling power of the junction valid for arbitrary time dependence of the Josephson phase. Combining it with the classical equation of motion for the phase, we find the time-averaged cooling power as a function of bias current or bias voltage. We also find the noise of the heat current and, more generally, the full counting statistics of the heat transport through the junction. We separately consider the metastable superconducting branch of the current-voltage characteristics allowing quantum fluctuations of the phase in this case. This regime is experimentally attractive since the junction has low power dissipation, low impedance, and therefore may be used as a sensitive detector.Item Induced unconventional superconductivity on the surface states of Bi2Te3 topological insulator(2017-12-01) Charpentier, Sophie; Galletti, Luca; Kunakova, Gunta; Arpaia, Riccardo; Song, Yuxin; Baghdadi, Reza; Wang, Shu Min; Kalaboukhov, Alexei; Olsson, Eva; Tafuri, Francesco; Golubev, Dmitry; Linder, Jacob; Bauch, Thilo; Lombardi, Floriana; Department of Applied Physics; Quantum Phenomena and Devices; Chalmers University of Technology; University of Naples Federico II; Norwegian University of Science and TechnologyTopological superconductivity is central to a variety of novel phenomena involving the interplay between topologically ordered phases and broken-symmetry states. The key ingredient is an unconventional order parameter, with an orbital component containing a chiral p x + ip y wave term. Here we present phase-sensitive measurements, based on the quantum interference in nanoscale Josephson junctions, realized by using Bi2Te3 topological insulator. We demonstrate that the induced superconductivity is unconventional and consistent with a sign-changing order parameter, such as a chiral p x + ip y component. The magnetic field pattern of the junctions shows a dip at zero externally applied magnetic field, which is an incontrovertible signature of the simultaneous existence of 0 and π coupling within the junction, inherent to a non trivial order parameter phase. The nano-textured morphology of the Bi2Te3 flakes, and the dramatic role played by thermal strain are the surprising key factors for the display of an unconventional induced order parameter.Item Noise of a superconducting magnetic flux sensor based on a proximity Josephson junction(2017-08-14) Najafi Jabdaraghi, Robab; Golubev, Dmitry; Pekola, J.P.; Peltonen, Joonas; Department of Applied PhysicsWe demonstrate simultaneous measurements of DC transport properties and flux noise of a hybrid superconducting magnetometer based on the proximity effect (superconducting quantum interference proximity transistor, SQUIPT). The noise is probed by a cryogenic amplifier operating in the frequency range of a few MHz. In our non-optimized device, we achieve minimum flux noise ~4 μΦ0/Hz1/2, set by the shot noise of the probe tunnel junction. The flux noise performance can be improved by further optimization of the SQUIPT parameters, primarily minimization of the proximity junction length and cross section. Furthermore, the experiment demonstrates that the setup can be used to investigate shot noise in other nonlinear devices with high impedance. This technique opens the opportunity to measure sensitive magnetometers including SQUIPT devices with very low dissipation.Item Statistics of heat exchange between two resistors(2015-08-10) Golubev, Dmitry; Pekola, Jukka; Department of Applied Physics; Quantum Phenomena and DevicesWe study energy flow between two resistors coupled by an arbitrary linear and lossless electric circuit. We show that the fluctuations of energy transferred between the resistors are determined by random scattering of photons on an effective barrier with frequency dependent transmission probability τ(ω). We express the latter in terms of the circuit parameters. Our results are valid in both quantum and classical regimes and for nonequilibrium electron distribution functions in the resistors. Our theory is in good agreement with recent experiment performed in the classical regime.Item Topological insulator nanoribbon Josephson junctions(American Institute of Physics, 2020-11-21) Kunakova, Gunta; Surendran, Ananthu P.; Montemurro, Domenico; Salvato, Matteo; Golubev, Dmitry; Andzane, Jana; Erts, Donats; Bauch, Thilo; Lombardi, Floriana; Chalmers University of Technology; University of Rome Tor Vergata; Centre of Excellence in Quantum Technology, QTF; University of Latvia; Department of Applied PhysicsWe have used Bi 2 Se 3 nanoribbons, grown by catalyst-free physical vapor deposition to fabricate high quality Josephson junctions with Al superconducting electrodes. In our devices, we observe a pronounced reduction of the Josephson critical current density J c by reducing the width of the junction, which in our case corresponds to the width of the nanoribbon. Because the topological surface states extend over the entire circumference of the nanoribbon, the superconducting transport associated with them is carried by modes on both the top and bottom surfaces of the nanoribbon. We show that the J c reduction as a function of the nanoribbon width can be accounted for by assuming that only the modes traveling on the top surface contribute to the Josephson transport as we derive by geometrical consideration. This finding is of great relevance for topological quantum circuitry schemes since it indicates that the Josephson current is mainly carried by the topological surface states.Item Towards microwave optomechanics using a superconducting carbon nanotube weak link(2019-07) Will, Marco; Kaikkonen, Jukka-Pekka; Golubev, Dmitry; Liao, Yongping; Laiho, Patrik; Thanniyil Sebastian, Abhilash; Hakonen, Pertti J.; Centre of Excellence in Quantum Technology, QTF; NanoMaterials; Department of Applied PhysicsUtilizing the ultra-high sensitivity of a superconducting single-walled carbon nanotube (SWCNT) sensor to probe the quantum ground state is a promising experimental approach for investigations of macroscopic quantum phenomena. However, reproducible and reliable fabrication of such devices is still to be shown due to the demands on high temperature stable materials that the SWCNT growth requires and the crucial role the contact resistance plays for inducing superconductivity into the SWCNT. We approach the challenge with suspended, 300nm long SWCNT contacted on MoRe leads. Good transparency of the superconductor-nanotube contacts allows observation of proxomity induced supercurrents of up to 50 nA, tuneable by gate induced charge. Additionally, we have developed a method to pick-up and place individual suspended SWCNT selectively on metal-electrodes. Using such weak links in an optomechanical microwave setting, coupling energies on the order of 100 kHz can be reached between the mechanical resonator and the electrical cavityItem Tunneling and relaxation of single quasiparticles in a normal-superconductor-normal single-electron transistor(2014-01-14) Heimes, Andreas; Maisi, Ville; Golubev, Dmitry; Marthaler, Michael; Schoen, Gerd; Pekola, Jukka P.; O.V.Lounasmaa-laboratorio; Quantum Phenomena and DevicesWe investigate the properties of a hybrid single-electron transistor, involving a small superconducting island sandwiched between normal metal leads, which is driven by dc plus ac voltages. In order to describe its properties we derive from the microscopic theory a set of coupled equations. They consist of a master equation for the probability to find excess charges on the island, with rates depending on the distribution of nonequilibrium quasiparticles. Their dynamics follows from a kinetic equation which accounts for the excitation by single-electron tunneling as well as the relaxation and eventual recombination due to the interaction with phonons. Our low-temperature results compare well with recent experimental findings obtained for ac-driven hybrid single-electron turnstiles.Item Wideband superconducting nanotube electrometer(2015) Häkkinen, Pasi; Fay, Aurélien; Golubev, Dmitry; Lähteenmäki, Pasi; Hakonen, Pertti; Department of Applied Physics; O.V.Lounasmaa-laboratorioWe have investigated the microwave response of nanotube Josephson junctions at 600–900 MHz at microwave powers corresponding to currents from 0 to 2 × I C in the junction. Compared with theoretical modeling, the response of the junctions corresponds well to the lumped element model of resistively and capacitively shunted junction. We demonstrate the operation of these superconducting FETs as charge detectors at high frequencies without any matching circuits. Gate-voltage-induced charge Q G modifies the critical current I C, which changes the effective impedance of the junction under microwave irradiation. This change, dependent on the transfer characteristics dI C/dQ G, modifies the reflected signal and it can be used for wide band electrometry. We measure a sensitivity of 3.1×10−5 e/Hz√ from a sample which has a maximum switching current of 2.6 nA.