Showing 1–19 of 19 results for author: Eyal, A

Experimental evidence of Tc enhancement above 50 K and diode and paramagnetic-Meissner effects, in Nickelate films on highly reduced $SrTiO_3$

Authors: Anna Eyal, Gad Koren

Abstract: Since the discovery of superconductivity in nickelate thin films in 2019, the quest for enhancing their $\mathrm{T}_\mathrm{c}$ has been ongoing. Here we provide experimental evidence for $\mathrm{T}_\mathrm{c}$ enhancement in oxygen deficient films on highly reduced and conducting SrTiO$_3$ substrates. $\mathrm{T}_\mathrm{c}$ onset of 50-70 K was found in Meissner and transport measurements, whic… ▽ More Since the discovery of superconductivity in nickelate thin films in 2019, the quest for enhancing their $\mathrm{T}_\mathrm{c}$ has been ongoing. Here we provide experimental evidence for $\mathrm{T}_\mathrm{c}$ enhancement in oxygen deficient films on highly reduced and conducting SrTiO$_3$ substrates. $\mathrm{T}_\mathrm{c}$ onset of 50-70 K was found in Meissner and transport measurements, which indicates superconductivity in islands or domains in our films, where $\mathrm{T}_\mathrm{c}$ of zero resistance is obtained at 20-25 K. In addition, we observed a giant paramagnetic-Meissner effect peak at about 48 K, which further supports the existence of a superconductive transition just above it. Furthermore, an asymmetric or nonreciprocal and non-hysteretic superconductive diode effect was observed. The latter effect could be fully polarized, and its polarity could be reversed. Our mixed phase films comprised of many Ruddlesden-Popper $\rm (Nd_{0.8}Sr_{0.2})_{n+1}Ni_nO_{3n+1}$ phases and includes the infinite-layer (IL) phase. △ Less

Submitted 21 June, 2026; v1 submitted 25 February, 2025; originally announced February 2025.

Comments: In this v3 version we include new STEM results of our virgin films, and extend our analysis of all FFT-STEM results. We found that our mixed-phase films comprise of various RP and IL phases

Intertwined topological phases in TaAs2 nanowires with giant magnetoresistance and quantum coherent surface transport

Authors: Anand Roy, Anna Eyal, Roni Majlin Skiff, Barun Barick, Samuel D. Escribano, Olga Brontvein, Katya Rechav, Ora Bitton, Roni Ilan, Ernesto Joselevich

Abstract: Nanowires (NWs) of topological materials are emerging as an exciting platform to probe and engineer new quantum phenomena that are hard to access in bulk phase. Their quasi-one-dimensional geometry and large surface-to-bulk ratio unlock new expressions of topology and highlight surface states. TaAs2, a compensated semimetal, is a topologically rich material harboring nodal-line, weak topological i… ▽ More Nanowires (NWs) of topological materials are emerging as an exciting platform to probe and engineer new quantum phenomena that are hard to access in bulk phase. Their quasi-one-dimensional geometry and large surface-to-bulk ratio unlock new expressions of topology and highlight surface states. TaAs2, a compensated semimetal, is a topologically rich material harboring nodal-line, weak topological insulator (WTI), C2-protected topological crystalline insulator, and Zeeman field-induced Weyl semimetal phases. We report the synthesis of TaAs2 NWs in situ encapsulated in a dielectric SiO2 shell, which enabled us to probe rich magnetotransport phenomena, including metal-to-insulator transition and strong signatures of topologically non-trivial transport at remarkably high temperatures, direction-dependent giant positive and negative magnetoresistance, and a double pattern of Aharonov-Bohm oscillations, demonstrating coherent surface transport consistent with the two Dirac cones of a WTI surface. The coexistence and susceptibility of topological phases to external stimuli have potential applications in spintronics and nanoscale quantum technology. △ Less

Submitted 24 November, 2024; originally announced November 2024.

Comments: 23 PAGES, 04 FIGURES

Change in Magnetic Order in NiPS3 Single Crystals Induced by a Molecular Intercalation

Authors: Nirman Chakraborty, Adi Harchol, Azhar Abu-Hariri, Rajesh Kumar Yadav, Muhamed Dawod, Diksha Prabhu Gaonkar, Kusha Sharma, Anna Eyal, Yaron Amouyal, Doron Naveh, Efrat Lifshitz

Abstract: Intercalation is a robust method for tuning the physical properties of a vast number of van der Waals (vdW) materials. However, the prospects of using intercalation to modify magnetism in vdWs systems and the associated mechanisms have not been investigated adequately. In this work, we modulate magnetic order in an XY antiferromagnet NiPS3 single crystals by introducing pyridine molecules into the… ▽ More Intercalation is a robust method for tuning the physical properties of a vast number of van der Waals (vdW) materials. However, the prospects of using intercalation to modify magnetism in vdWs systems and the associated mechanisms have not been investigated adequately. In this work, we modulate magnetic order in an XY antiferromagnet NiPS3 single crystals by introducing pyridine molecules into the vdWs gap under different thermal conditions. X-ray diffraction measurements indicated pronounced changes in the lattice parameter beta, while magnetization measurements at in-plane and out-of-plane configurations exposed reversal trends in the crystals Neel temperatures through intercalation-de-intercalation processes. The changes in magnetic ordering were also supported by three-dimensional thermal diffusivity experiments. The preferred orientation of the pyridine dipoles within vdW gaps was deciphered via polarized Raman spectroscopy. The results highlight the relation between the preferential alignment of the intercalants, thermal transport, and crystallographic disorder along with the modulation of anisotropy in the magnetic order. The theoretical concept of double-exchange interaction in NiPS3 was employed to explain the intercalation-induced magnetic ordering. The study uncovers the merit of intercalation as a foundation for spin switches and spin transistors in advanced quantum devices. △ Less

Submitted 15 October, 2024; originally announced October 2024.

Journal ref: Chemistry of Materials, 2025

Magnetic Order and Magneto-Elasticity in the Electronic Excitations of Gd-$i$-MAX

Authors: Kartik Panda, Daniel Potashnikov, Asaf Pesach, Maxime Barbier, Anna Eyal, Thierry Ouisse, Amit Keren, Nimrod Bachar

Abstract: We report the investigation of electronic collective modes in rare-earth-based magnets (Mo$_{2/3}$RE$_{1/3}$)$_2$AlC (also known as RE-$i$-MAX phases), where RE=Gd, Yb, and Dy, using single crystal samples. A detailed investigation of the Raman spectra of Gd-$i$-MAX samples at low temperatures, with a focus on the phonon behavior in relation to the antiferromagnetic (AFM) phase transition at 26 K… ▽ More We report the investigation of electronic collective modes in rare-earth-based magnets (Mo$_{2/3}$RE$_{1/3}$)$_2$AlC (also known as RE-$i$-MAX phases), where RE=Gd, Yb, and Dy, using single crystal samples. A detailed investigation of the Raman spectra of Gd-$i$-MAX samples at low temperatures, with a focus on the phonon behavior in relation to the antiferromagnetic (AFM) phase transition at 26 K is presented. Significant shifts in the central frequencies of several low-frequency phonon modes were observed below 25 K, correlating with the Néel transition. Integrated Raman intensity measurements indicated a reduction in the electronic background below the AFM transition temperature, suggesting the opening of a magnetic gap. Our analysis showed no new phonon modes. Therefore, we do not see any indication of a Brillouin zone folding of phonon mode to the $Γ$-point in our measurement. However, the hardening of all phonon modes at low temperatures points to a strong spin-phonon coupling effect. Using a temperature-dependent model of phonon frequency, we determined the spin-phonon coupling constant $λ$ to be less than 0.1 cm$^{-1}$ for all frequencies, which is of the same order of magnitude as found in other antiferromagnetic materials such as MnF$_{2}$ and FeF$_{2}$ with $T_N=68~K$ and $T_N=78~K$, respectively, but significantly lower than that of $CuO$ with $T_N=213~K$. △ Less

Submitted 5 August, 2024; originally announced August 2024.

Comments: 9 pages, 13 figures

Tuning Magnetic and Optical Properties in MnxZn1-xPS3 Single Crystals by the Alloying Composition

Authors: Adi Harchol, Shahar Zuri, Esther Ritov, Faris Horani, Miłosz Rybak, Tomasz Woźniak, Anna Eyal, Yaron Amouyal, Magdalena Birowska, Efrat Lifshitz

Abstract: The exploration of two-dimensional (2D) antiferromagnetic (AFM) materials has shown great promise and interest in tuning the magnetic and electronic properties as well as studying magneto-optical effects. The current work investigates the control of magneto-optical interactions in alloyed MnxZn1-xPS3 lamellar semiconductor single crystals, with the Mn/Zn ratio regulating the coupling strength. Mag… ▽ More The exploration of two-dimensional (2D) antiferromagnetic (AFM) materials has shown great promise and interest in tuning the magnetic and electronic properties as well as studying magneto-optical effects. The current work investigates the control of magneto-optical interactions in alloyed MnxZn1-xPS3 lamellar semiconductor single crystals, with the Mn/Zn ratio regulating the coupling strength. Magnetic susceptibility results show a retention of AFM order followed by a decrease in Néel temperatures down to ~ 40% Mn concentration, below which a paramagnetic behavior is observed. Absorption measurements reveal an increase in bandgap energy with higher Zn(II) concentration, and the presence of Mn(II) d-d transition below the absorption edge. DFT+U approach qualitatively explained the origin and the position of the experimentally observed mid band-gap states in pure MnPS3, and corresponding peaks visible in the alloyed systems MnxZn1-xPS3. Accordingly, emission at 1.3 eV in all alloyed compounds results from recombination from a 4T1g Mn(II) excited state to a hybrid p-d state at the valence band. Most significant, temperature-dependent photoluminescence (PL) intensity trends demonstrate strong magneto-optical coupling in compositions with x > 0.65. This study underscores the potential of tailored alloy compositions as a means to control magnetic and optical properties in 2D materials, paving the way for advances in spin-based technologies. △ Less

Submitted 11 April, 2024; originally announced April 2024.

Supercooling of the A phase of $^3$He

Authors: Yefan Tian, Dmytro Lotnyk, Anna Eyal, Kuang Zhang, Nikolay Zhelev, T. S. Abhilash, Aldo Chavez, Eric Smith, Mark Hindmarsh, John Saunders, Erich Mueller, Jeevak Parpia

Abstract: Because of the extreme purity, lack of disorder, and complex order parameter, the first-order superfluid $^3$He A-B transition is the leading model system for first order transitions in the early universe. Here we report on the path dependence of the supercooling of the A phase over a wide range of pressures below 29.3 bar at nearly zero magnetic field. The A phase can be cooled significantly belo… ▽ More Because of the extreme purity, lack of disorder, and complex order parameter, the first-order superfluid $^3$He A-B transition is the leading model system for first order transitions in the early universe. Here we report on the path dependence of the supercooling of the A phase over a wide range of pressures below 29.3 bar at nearly zero magnetic field. The A phase can be cooled significantly below the thermodynamic A-B transition temperature. While the extent of supercooling is highly reproducible, it depends strongly upon the cooling trajectory: The metastability of the A phase is enhanced by transiting through regions where the A phase is more stable. We provide evidence that some of the additional supercooling is due to the elimination of B phase seeds formed upon passage through the superfluid transition. A greater understanding of the physics is essential before the $^3$He can be exploited to model transitions in the early universe. △ Less

Submitted 25 August, 2022; originally announced August 2022.

Comments: 6 Figures

Path-Dependent Supercooling of the $^3$He Superfluid A-B transition

Authors: Dmytro Lotnyk, Anna Eyal, Nikolay Zhelev, Abhilash Sebastian, Yefan Tian, Aldo Chavez, Eric Smith, John Saunders, Erich Mueller, Jeevak Parpia

Abstract: We examine the discontinuous first-order superfluid $^3$He A to B transition in the vicinity of the polycritical point (2.232 mK and 21.22 bar). We find path-dependent transitions: cooling at fixed pressure yields a well defined transition line in the temperature-pressure plane, but this line can be reliably crossed by depressurizing at nearly constant temperature after transiting $T_{\rm c}$ at a… ▽ More We examine the discontinuous first-order superfluid $^3$He A to B transition in the vicinity of the polycritical point (2.232 mK and 21.22 bar). We find path-dependent transitions: cooling at fixed pressure yields a well defined transition line in the temperature-pressure plane, but this line can be reliably crossed by depressurizing at nearly constant temperature after transiting $T_{\rm c}$ at a higher pressure. This path dependence is not consistent with any of the standard B-phase nucleation mechanisms in the literature. This symmetry breaking transition is a potential simulator for first order transitions in the early universe. △ Less

Submitted 2 April, 2021; v1 submitted 27 December, 2020; originally announced December 2020.

Journal ref: Phys. Rev. Lett. 126, 215301 (2021)

Observation of Josephson-like tunneling junction characteristics and positive magnetoresistance in Oxygen deficient Nickelate films of $Nd_{0.8}Sr_{0.2}NiO_{3-δ}$

Authors: Gad Koren, Anna Eyal, Leonid Iomin, Yuval Nitzav

Abstract: Nickelate films have recently attracted broad attention due to the observation of superconductivity in the infinite layer phase of $Nd_{0.8}Sr_{0.2}NiO_2$ (obtained by reducing Sr doped $NdNiO_3$ films) and their similarity to the cuprates high temperature superconductors. Here we report on the observation of a new type of transport in oxygen poor $Nd_{0.8}Sr_{0.2}NiO_{3-δ}$ films. At high tempera… ▽ More Nickelate films have recently attracted broad attention due to the observation of superconductivity in the infinite layer phase of $Nd_{0.8}Sr_{0.2}NiO_2$ (obtained by reducing Sr doped $NdNiO_3$ films) and their similarity to the cuprates high temperature superconductors. Here we report on the observation of a new type of transport in oxygen poor $Nd_{0.8}Sr_{0.2}NiO_{3-δ}$ films. At high temperatures, variable range hopping is observed while at low temperatures a novel tunneling behavior is found where Josephson-like tunneling junction characteristic with serial resistance is revealed. We attribute this phenomenon to coupling between superconductive (S) surfaces of the grains in our Oxygen poor films via the insulating (I) grain boundaries, which yields SIS junctions in series with the normal (N) resistance of the grains themselves. The similarity of the observed conductance spectra to tunneling junction characteristic with Josephson-like current is striking, and seems to support the existence of superconductivity in our samples. △ Less

Submitted 3 December, 2020; v1 submitted 11 October, 2020; originally announced October 2020.

Comments: This version includes: 1. A new Fig, 1 with the surface morphology and a surface tunneling model. 2. Fig. 2 of the XRD now shows more details including minority Ni_xO_y phases. 3. More VRH models are now included in Fig. 4. 4. Extended conductance range in Fig. 6 (c) now shows the second quasi-particle branch more clearly

Journal ref: Materials 2021, vol 14, 7689

Magnetic properties of $(Fe_{1-x}Mn_x)_2AlB_2$ and the impact of substitution on the magnetocaloric effect

Authors: D. Potashnikov, E. N. Caspi, A. Pesach, S. Kota, M. Sokol, L. A. Hanner, M. W. Barsoum, H. A. Evans, A. Eyal, A. Keren, O. Rivin

Abstract: In this work, we investigate the magnetic structures of $(Fe_{1-x}Mn_x)_2AlB_2$ solid-solution quaternaries in the $x = 0$ to $1$ range using x-ray and neutron diffraction, magnetization measurements, and mean-field theory calculations. While $Fe_2AlB_2$ and $Mn_2AlB_2$ are known to be ferromagnetic (FM) and antiferromagnetic (AFM), respectively, herein we focused on the magnetic structure of thei… ▽ More In this work, we investigate the magnetic structures of $(Fe_{1-x}Mn_x)_2AlB_2$ solid-solution quaternaries in the $x = 0$ to $1$ range using x-ray and neutron diffraction, magnetization measurements, and mean-field theory calculations. While $Fe_2AlB_2$ and $Mn_2AlB_2$ are known to be ferromagnetic (FM) and antiferromagnetic (AFM), respectively, herein we focused on the magnetic structure of their solid solutions, which is not well understood. The FM ground state of $Fe_2AlB_2$ becomes a canted AFM at $x \approx 0.2$, with a monotonically diminishing FM component until $x \approx 0.5$. The FM transition temperature ($T_C$) decreases linearly with increasing $x$. These changes in magnetic moments and structures are reflected in anomalous expansions of the lattice parameters, indicating a magnetoelastic coupling. Lastly, the magnetocaloric properties of the solid solutions were explored. For $x = 0.2$ the isothermal entropy change is smaller by 30% than it is for $Fe_2AlB_2$, while the relative cooling power is larger by 6%, due to broadening of the temperature range of the transition. △ Less

Submitted 7 August, 2020; v1 submitted 15 July, 2020; originally announced July 2020.

Comments: Final version as published in physical review materials

Journal ref: Phys. Rev. Materials 4, 084404 (2020)

Thermal transport of helium-3 in a strongly confining channel

Authors: D. Lotnyk, A. Eyal, N. Zhelev, T. S. Abhilash, E. N. Smith, M. Terilli, J. Wilson, E. Mueller, D. Einzel, J. Saunders, J. M. Parpia

Abstract: In a neutral system such as liquid helium-3, transport of mass, heat, and spin provide information analogous to electrical counterparts in metals, superconductors and topological materials. Of particular interest is transport in strongly confining channels of height approaching the superfluid coherence length, where new quantum states are found and excitations bound to surfaces and edges should be… ▽ More In a neutral system such as liquid helium-3, transport of mass, heat, and spin provide information analogous to electrical counterparts in metals, superconductors and topological materials. Of particular interest is transport in strongly confining channels of height approaching the superfluid coherence length, where new quantum states are found and excitations bound to surfaces and edges should be present. Here we report on the thermal conduction of helium-3 in a 1.1~$μ$m high microfabricated channel. In the normal state we observe a diffusive thermal conductivity that is approximately temperature independent, consistent with recent work on the interference of bulk and boundary scattering. In the superfluid state we measure diffusive thermal transport in the absence of thermal counterflow. An anomalous thermal response is also detected in the superfluid which we suggest may arise from a flux of surface excitations. △ Less

Submitted 18 October, 2019; originally announced October 2019.

Comments: A supplement is available. Please contact Jeevak Parpia (jmp9@cornell.edu) if you would like the supplement as well

Magnetic Monopole Noise

Authors: Ritika Dusad, Franziska K. K. Kirschner, Jesse C. Hoke, Benjamin Roberts, Anna Eyal, Felix Flicker, Graeme M. Luke, Stephen J. Blundell, J. C. Seamus Davis

Abstract: Magnetic monopoles are hypothetical elementary particles exhibiting quantized magnetic charge $m_0=\pm(h/μ_0e)$ and quantized magnetic flux $Φ_0=\pm h/e$. A classic proposal for detecting such magnetic charges is to measure the quantized jump in magnetic flux $Φ$ threading the loop of a superconducting quantum interference device (SQUID) when a monopole passes through it. Naturally, with the theor… ▽ More Magnetic monopoles are hypothetical elementary particles exhibiting quantized magnetic charge $m_0=\pm(h/μ_0e)$ and quantized magnetic flux $Φ_0=\pm h/e$. A classic proposal for detecting such magnetic charges is to measure the quantized jump in magnetic flux $Φ$ threading the loop of a superconducting quantum interference device (SQUID) when a monopole passes through it. Naturally, with the theoretical discovery that a plasma of emergent magnetic charges should exist in several lanthanide-pyrochlore magnetic insulators, including Dy$_2$Ti$_2$O$_7$, this SQUID technique was proposed for their direct detection. Experimentally, this has proven extremely challenging because of the high number density, and the generation-recombination (GR) fluctuations, of the monopole plasma. Recently, however, theoretical advances have allowed the spectral density of magnetic-flux noise $S_Φ(ω,T)$ due to GR fluctuations of $\pm m_*$ magnetic charge pairs to be determined. These theories present a sequence of strikingly clear predictions for the magnetic-flux noise signature of emergent magnetic monopoles. Here we report development of a high-sensitivity, SQUID based flux-noise spectrometer, and consequent measurements of the frequency and temperature dependence of $S_Φ(ω,T)$ for Dy$_2$Ti$_2$O$_7$ samples. Virtually all the elements of $S_Φ(ω,T)$ predicted for a magnetic monopole plasma, including the existence of intense magnetization noise and its characteristic frequency and temperature dependence, are detected directly. Moreover, comparisons of simulated and measured correlation functions $C_Φ(t)$ of the magnetic-flux noise $Φ(t)$ imply that the motion of magnetic charges is strongly correlated because traversal of the same trajectory by two magnetic charges of same sign is forbidden. △ Less

Submitted 24 April, 2019; v1 submitted 28 January, 2019; originally announced January 2019.

Journal ref: Nature (2019)

Common Glass-Forming Spin-Liquid State in the Pyrochlore Magnets Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$

Authors: Azar B. Eyvazov, Ritika Dusad, Timothy J. S. Munsie, Hanna A. Dabkowska, Graeme M. Luke, Ethan R. Kassner, J. C. Séamus Davis, Anna Eyal

Abstract: Despite a well-ordered pyrochlore crystal structure and strong magnetic interactions between the Dy$^{3+}$ or Ho$^{3+}$ ions, no long range magnetic order has been detected in the pyrochlore titanates Ho$_2$Ti$_2$O$_7$ and Dy$_2$Ti$_2$O$_7$. To explore the actual magnetic phase formed by cooling these materials, we measure their magnetization dynamics using toroidal, boundary-free magnetization tr… ▽ More Despite a well-ordered pyrochlore crystal structure and strong magnetic interactions between the Dy$^{3+}$ or Ho$^{3+}$ ions, no long range magnetic order has been detected in the pyrochlore titanates Ho$_2$Ti$_2$O$_7$ and Dy$_2$Ti$_2$O$_7$. To explore the actual magnetic phase formed by cooling these materials, we measure their magnetization dynamics using toroidal, boundary-free magnetization transport techniques. We find that the dynamical magnetic susceptibility of both compounds has the same distinctive phenomenology, that is indistinguishable in form from that of the dielectric permittivity of dipolar glass-forming liquids. Moreover, Ho$_2$Ti$_2$O$_7$ and Dy$_2$Ti$_2$O$_7$ both exhibit microscopic magnetic relaxation times that increase along the super-Arrhenius trajectories analogous to those observed in glass-forming dipolar liquids. Thus, upon cooling below about 2K, Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$ both appear to enter the same magnetic state exhibiting the characteristics of a glass-forming spin-liquid. △ Less

Submitted 27 November, 2018; v1 submitted 27 July, 2017; originally announced July 2017.

Comments: 9 pages, 4 figures

Journal ref: Phys. Rev. B 98, 214430 (2018)

Multiple Mode Torsional Oscillator Studies and Evidence for Supersolidity in Bulk 4He

Authors: Anna Eyal, Xiao Mi, Artem V. Talanov, John D. Reppy

Abstract: The discovery by Kim and Chan (KC) of an anomalous decrease in the period of torsional oscillators (TO) containing samples of solid $^4$He at temperatures below 0.2 K was initially interpreted as a superfluid-like decoupling of a fraction of the solid moment of inertia from the TO. These experiments appeared to confirm the thirty-year-old theoretical prediction by Chester, Andreev, and Leggett of… ▽ More The discovery by Kim and Chan (KC) of an anomalous decrease in the period of torsional oscillators (TO) containing samples of solid $^4$He at temperatures below 0.2 K was initially interpreted as a superfluid-like decoupling of a fraction of the solid moment of inertia from the TO. These experiments appeared to confirm the thirty-year-old theoretical prediction by Chester, Andreev, and Leggett of the existence of a low-temperature Bose-condensed supersolid phase in solid $^4$He. The initial results of KC lead to a flurry of experimental and theoretical activity and their results for bulk $^4$He samples were soon confirmed in a number of laboratories. The early excitement in this field, however, has been tempered by the realization that an anomaly in the shear modulus of solid helium $^4$He may explain most if not all of the period shifts observed in the early TO experiments. In principle, it is possible to distinguish experimentally between shear modulus induced period shifts and period shifts resulting from other physical mechanisms through the use of multiple frequency torsional oscillators. In this paper we shall discuss our recent results on bulk solid $^4$He with double and triple mode TOs, using both open cylindrical cells and annular cells. In these experiments, we have observed a small frequency independent contribution to the period shift signal such as might be expected in the presence of a supersolid phase. Since the interplay between the elastic properties of the solid and the mechanics of TOs can be subtle and depends on the specific design of the TO, we shall discuss in detail the mechanics of the TOs employed in our measurements applying both analytic and finite element methods (FEM) for the analysis. △ Less

Submitted 11 November, 2015; originally announced November 2015.

Comments: 19 pages, 18 figures

Journal ref: PNAS vol. 113 no. 23 E3203 (2016)

Characterization of the Surface of Moving solid 4He

Authors: Ethan Livne, Anna Eyal, Ori Scaly, Emil Polturak

Abstract: Crystal grains of solid $^4$He can move in relation to each other even when embedded inside the solid. In this work, we characterize a macroscopic motion of solid hcp $^4$He composed of such grains. Motion is induced by applying an external torque to the solid contained inside an annular channel mounted on a torsional oscillator. In order to characterize the surface of the moving solid, we develop… ▽ More Crystal grains of solid $^4$He can move in relation to each other even when embedded inside the solid. In this work, we characterize a macroscopic motion of solid hcp $^4$He composed of such grains. Motion is induced by applying an external torque to the solid contained inside an annular channel mounted on a torsional oscillator. In order to characterize the surface of the moving solid, we developed an in-situ flow detection method using a sensitive "microphone" embedded in the wall of the channel. Motion is detected by counting the vibrations induced by rows of He atoms moving past the microphone. Such vibrations were detected only at T=0.5K, our lowest temperature. At this temperature, the measured dissipation associated with the solid He is zero within our accuracy. Our results indicate that the orientation of the surface of the moving solid is the (0001) basal plane of the hcp structure. At T=0.5 K, we found that for speeds < 7 micrometer/sec, the solid flows without detectable friction. △ Less

Submitted 7 April, 2015; originally announced April 2015.

Comments: 17 pages, 9 figures

Evidence for Supersolidity in Bulk Solid $^4$He

Authors: Xiao Mi, Anna Eyal, Artem V. Talanov, John D. Reppy

Abstract: We report low temperature measurements of bulk solid $^4$He in a two-frequency compound torsional oscillator with both annular and open cylinder sample geometries. The oscillators were designed to suppress period shifts arising from all known elastic effects of solid $^4$He. At temperatures below 0.25 K, period shift signals similar to those reported by Kim and Chan [Science {\bf 305}, 1941 (2004)… ▽ More We report low temperature measurements of bulk solid $^4$He in a two-frequency compound torsional oscillator with both annular and open cylinder sample geometries. The oscillators were designed to suppress period shifts arising from all known elastic effects of solid $^4$He. At temperatures below 0.25 K, period shift signals similar to those reported by Kim and Chan [Science {\bf 305}, 1941 (2004)] were observed, albeit two orders smaller in magnitude. A sizable fraction of the observed signals are frequency-independent and consistent with the mass-decoupling expected for supersolid $^4$He. This result is in stark contrast with recent works on Vycor-solid-$^4$He system and suggests that a small supersolid fraction on the order of $1 \times 10^{-4}$ may indeed exist in bulk solid $^4$He. △ Less

Submitted 6 July, 2014; originally announced July 2014.

Comments: 5 pages, 5 figures, Supplement 4 pages, 2 figures

Observation of a Dislocation Related Interfacial Friction Mechanism in Mobile Solid $^4$He

Authors: Anna Eyal, Ethan Livne, Emil Polturak

Abstract: We report a study of the temperature and stress dependence of the friction associated with a relative motion of two masses of solid $^4$He in contact. The situation where "two masses" coupled only by friction exists emerges spontaneously during a disordering of a single crystal contained inside a annular sample space of torsional oscillator (TO). Under the torque applied by the oscillating walls o… ▽ More We report a study of the temperature and stress dependence of the friction associated with a relative motion of two masses of solid $^4$He in contact. The situation where "two masses" coupled only by friction exists emerges spontaneously during a disordering of a single crystal contained inside a annular sample space of torsional oscillator (TO). Under the torque applied by the oscillating walls of the the TO these "masses" move relative to each other, generating measurable dissipation at their interface. We studied this dissipation between 0.5K and 1.8K in solid samples grown from commercially pure $^4$He and from a 100 ppm $^3$He-$^4$He mixture. The data were analyzed by modelling the TO as a driven harmonic oscillator. In this model, analysis of the resonant frequency and amplitude of the TO yields the temperature dependence of the friction coefficient. By fitting the data to specific forms, we found that over our temperature range, the dominant friction mechanism associated with the interfacial motion results from climb of individual dislocations. The characteristic energy scale associated with this internal friction is between 3K and 6K, depending on the sample. The fact that a single value of this energy accounts for the data of a given sample supports the idea that the interface between the moving and static solid is well oriented. The relative motion of the solid in this case can perhaps be described as the low limit of "slip-stick" motion. △ Less

Submitted 15 July, 2015; v1 submitted 5 June, 2012; originally announced June 2012.

Comments: 10 pages, 5 figures

BCC vs. HCP - The Effect of Crystal Symmetry on the High Temperature Mobility of Solid $^4$He

Authors: Anna Eyal, Emil Polturak

Abstract: We report results of torsional oscillator (TO) experiments on solid $^4$He at temperatures above 1K. We have previously found that single crystals, once disordered, show some mobility (decoupled mass) even at these rather high temperatures. The decoupled mass fraction with single crystals is typically 20- 30%. In the present work we performed similar measurements on polycrystalline solid samples.… ▽ More We report results of torsional oscillator (TO) experiments on solid $^4$He at temperatures above 1K. We have previously found that single crystals, once disordered, show some mobility (decoupled mass) even at these rather high temperatures. The decoupled mass fraction with single crystals is typically 20- 30%. In the present work we performed similar measurements on polycrystalline solid samples. The decoupled mass with polycrystals is much smaller, $\sim$ 1%, similar to what is observed by other groups. In particular, we compared the properties of samples grown with the TO's rotation axis at different orientations with respect to gravity. We found that the decoupled mass fraction of bcc samples is independent of the angle between the rotation axis and gravity. In contrast, hcp samples showed a significant difference in the fraction of decoupled mass as the angle between the rotation axis and gravity was varied between zero and 85 degrees. Dislocation dynamics in the solid offers one possible explanation of this anisotropy. △ Less

Submitted 7 February, 2012; originally announced February 2012.

Comments: 10 pages, 5 figures, to appear in Journal of Low Temperature Physics - special issue on Supersolidity

On The Mobile Behavior of Solid $^4$He at High Temperatures

Authors: Anna Eyal, Emil Polturak

Abstract: We report studies of solid helium contained inside a torsional oscillator, at temperatures between 1.07K and 1.87K. We grew single crystals inside the oscillator using commercially pure $^4$He and $^3$He-$^4$He mixtures containing 100 ppm $^3$He. Crystals were grown at constant temperature and pressure on the melting curve. At the end of the growth, the crystals were disordered, following which th… ▽ More We report studies of solid helium contained inside a torsional oscillator, at temperatures between 1.07K and 1.87K. We grew single crystals inside the oscillator using commercially pure $^4$He and $^3$He-$^4$He mixtures containing 100 ppm $^3$He. Crystals were grown at constant temperature and pressure on the melting curve. At the end of the growth, the crystals were disordered, following which they partially decoupled from the oscillator. The fraction of the decoupled He mass was temperature and velocity dependent. Around 1K, the decoupled mass fraction for crystals grown from the mixture reached a limiting value of around 35%. In the case of crystals grown using commercially pure $^4$He at temperatures below 1.3K, this fraction was much smaller. This difference could possibly be associated with the roughening transition at the solid-liquid interface. △ Less

Submitted 27 February, 2011; originally announced February 2011.

Comments: 15 pages, 6 figures

Evidence for a High-Temperature Disorder-Induced Mobility in Solid $^4$He

Authors: Anna Eyal, Oshri Pelleg, Lior Embon, Emil Polturak

Abstract: We have carried out torsional oscillator experiments on solid $^4$He at temperatures between 1.3K and 1.9K. We discovered phenomena similar to those observed at temperatures below 0.2K, which currently are under debate regarding their interpretation in terms of supersolidity. These phenomena include a partial decoupling of the solid helium mass from the oscillator, a change of the dissipation, and… ▽ More We have carried out torsional oscillator experiments on solid $^4$He at temperatures between 1.3K and 1.9K. We discovered phenomena similar to those observed at temperatures below 0.2K, which currently are under debate regarding their interpretation in terms of supersolidity. These phenomena include a partial decoupling of the solid helium mass from the oscillator, a change of the dissipation, and a velocity dependence of the decoupled mass. These were all observed both in the bcc and hcp phases of solid $^4$He. The onset of this behavior is coincidental with the creation of crystalline disorder but does not depend strongly on the crystalline symmetry or on the temperature. △ Less

Submitted 20 July, 2010; v1 submitted 18 March, 2010; originally announced March 2010.

Comments: 4 pages, 5 figures

Journal ref: Phys. Rev. Lett. 105, 025301 (2010)