HfO2, a simple binary oxide, exhibits ultra-scalable ferroelectricity integrable into silicon technology. This material has a polymorphic nature, with the polar orthorhombic (Pbc21) form in ultrathin ...films regarded as the plausible cause of ferroelectricity but thought not to be attainable in bulk crystals. Here, using a state-of-the-art laser-diode-heated floating zone technique, we report the Pbc21 phase and ferroelectricity in bulk single-crystalline HfO2:Y as well as the presence of the antipolar Pbca phase at different Y concentrations. Neutron diffraction and atomic imaging demonstrate (anti)polar crystallographic signatures and abundant 90°/180° ferroelectric domains in addition to switchable polarization with negligible wake-up effects. Density-functional-theory calculations indicate that the yttrium doping and rapid cooling are the key factors for stabilization of the desired phase in bulk. Our observations provide insights into the polymorphic nature and phase control of HfO2, remove the upper size limit for ferroelectricity and suggest directions towards next-generation ferroelectric devices.Hafnia ferroelectrics are of industrial interest owing to their compatibility with silicon-based electronics, but the ferroelectricity only exists in nanoscale films. Here, using a floating zone growth approach, ferroelectricity in bulk Y-doped hafnia is demonstrated.
Abstract
Chirality with all broken mirror symmetries matters ubiquitously from DNA functionality, vine climbing, to the piezoelectricity of quartz crystals. Magnetic chirality means chirality in ...spin-ordered states or (atomic-scale or mesoscopic) spin textures. Magnetic chirality does not change with time-reversal operation, and chirality prime (
$${\mathcal{C}}^\prime$$
C
′
) means that time-reversal symmetry in addition to all mirror symmetries is broken with free spatial rotations. We will discuss a few examples of magnetic chirality and
$${\mathcal{C}}^\prime$$
C
′
, and their emergent physical properties. Some of these exotic properties have been recently observed, and many of them need to be experimentally confirmed.
Abstract
Ferrotoroidal order, which represents a spontaneous arrangement of toroidal moments, has recently been found in a few linear magnetoelectric materials. However, tuning toroidal moments in ...these materials is challenging. Here, we report switching between ferritoroidal and ferrotoroidal phases by a small magnetic field, in a chiral triangular-lattice magnet BaCoSiO
4
with tri-spin vortices. Upon applying a magnetic field, we observe multi-stair metamagnetic transitions, characterized by equidistant steps in the net magnetic and toroidal moments. This highly unusual ferri-ferroic order appears to come as a result of an unusual hierarchy of frustrated isotropic exchange couplings revealed by first principle calculations, and the antisymmetric exchange interactions driven by the structural chirality. In contrast to the previously known toroidal materials identified via a linear magnetoelectric effect, BaCoSiO
4
is a qualitatively new multiferroic with an unusual coupling between several different orders, and opens up new avenues for realizing easily tunable toroidal orders.
A quantum spin liquid is a state of matter where unpaired electrons’ spins, although entangled, do not show magnetic order even at the zero temperature. The realization of a quantum spin liquid is a ...long-sought goal in condensed-matter physics. Although neutron scattering experiments on the two-dimensional spin-1/2 kagome lattice ZnCu3(OD)6Cl2 and triangular lattice YbMgGaO4 have found evidence for the hallmark of a quantum spin liquid at very low temperature (a continuum of magnetic excitations), the presence of magnetic and non-magnetic site chemical disorder complicates the interpretation of the data. Recently, the three-dimensional Ce3+ pyrochlore lattice Ce2Sn2O7 has been suggested as a clean, effective spin-1/2 quantum spin liquid candidate, but evidence of a spin excitation continuum is still missing. Here, we use thermodynamic, muon spin relaxation and neutron scattering experiments on single crystals of Ce2Zr2O7, a compound isostructural to Ce2Sn2O7, to demonstrate the absence of magnetic ordering and the presence of a spin excitation continuum at 35 mK. With no evidence of oxygen deficiency and magnetic/non-magnetic ion disorder seen by neutron diffraction and diffuse scattering measurements, Ce2Zr2O7 may be a three-dimensional pyrochlore lattice quantum spin liquid material with minimum magnetic and non-magnetic chemical disorder.
Abstract
Optical control of the spin degree of freedom is often desired in application of the spin technology. Here we report spin-rotational excitations observed through inelastic light scattering ...of the hexagonal LuMnO
3
in the antiferromagnetically (AFM) ordered state. We propose a model based on the spin–spin interaction Hamiltonian associated with the spin rotation of the Mn ions, and find that the spin rotations are angularly quantized by 60°, 120°, and 180°. Angular quantization is considered to be a consequence of the symmetry of the triangular lattice of the Mn-ion plane in the hexagonal LuMnO
3
. These angularly-quantized spin excitations may be pictured as isolated flat bubbles in the sea of the ground state, which may lead to high-density information storage if applied to spin devices. Optically pumped and detected spin-excitation bubbles would bring about the advanced technology of optical control of the spin degree of freedom in multiferroic materials.
Spin liquid ground states are predicted to arise within several distinct scenarios in condensed matter physics. The observation of these disordered magnetic states is particularly pervasive among a ...class of materials known as frustrated magnets, in which the competition between various magnetic exchange interactions prevents the system from adopting long-range magnetic order at low temperatures. Spin liquids continue to be of great interest due to their exotic nature and the possibility that they may support fractionalized excitations, such as Majorana fermions. Systems that allow for such phenomena are not only fascinating from a fundamental perspective but may also be practically significant in future technologies based on quantum computation. Here we show that the underlying antiferromagnetic sublattice in TbInO3 can undergo a crystal field-induced distortion of its buckled triangular arrangement to one based on a honeycomb. The absence of a conventional magnetic ordering transition at the lowest measurable temperatures indicates that another critical mechanism must govern in the ground-state selection of TbInO3. We suggest that anisotropic exchange interactions—mediated through strong spin–orbit coupling on the emergent honeycomb lattice of TbInO3—give rise to a highly frustrated spin liquid.Detailed neutron scattering, magnetic susceptibility and muon spin relaxation studies indicate the absence of long-range magnetic order in the quantum magnet TbInO3 down to 0.46 K— an observation consistent with quantum spin liquid behaviour.
Abstract
Hafnia (HfO
2
) is a promising material for emerging chip applications due to its high-
κ
dielectric behavior, suitability for negative capacitance heterostructures, scalable ...ferroelectricity, and silicon compatibility. The lattice dynamics along with phononic properties such as thermal conductivity, contraction, and heat capacity are under-explored, primarily due to the absence of high quality single crystals. Herein, we report the vibrational properties of a series of HfO
2
crystals stabilized with yttrium (chemical formula HfO
2
:
x
Y, where
x
= 20, 12, 11, 8, and 0%) and compare our findings with a symmetry analysis and lattice dynamics calculations. We untangle the effects of Y by testing our calculations against the measured Raman and infrared spectra of the cubic, antipolar orthorhombic, and monoclinic phases and then proceed to reveal the signature modes of polar orthorhombic hafnia. This work provides a spectroscopic fingerprint for several different phases of HfO
2
and paves the way for an analysis of mode contributions to high-
κ
dielectric and ferroelectric properties for chip technologies.
Abstract Nonreciprocal quantum transport effect is mainly governed by the symmetry breaking of the material systems and is gaining extensive attention in condensed matter physics. Realizing ...electrical switching of the polarity of the nonreciprocal transport without external magnetic field is essential to the development of nonreciprocal quantum devices. However, electrical switching of superconducting nonreciprocity remains yet to be achieved. Here, we report the observation of field-free electrical switching of nonreciprocal Ising superconductivity in Fe 3 GeTe 2 /NbSe 2 van der Waals (vdW) heterostructure. By taking advantage of this electrically switchable superconducting nonreciprocity, we demonstrate a proof-of-concept nonreciprocal quantum neuronal transistor, which allows for implementing the XOR logic gate and faithfully emulating biological functionality of a cortical neuron in the brain. Our work provides a promising pathway to realize field-free and electrically switchable nonreciprocity of quantum transport and demonstrate its potential in exploring neuromorphic quantum devices with both functionality and performance beyond the traditional devices.
Triangular lattice magnets have attracted extensive research interest because they are potential hosts for geometrically frustrated magnetism and strong quantum fluctuations. Here, utilizing a laser ...floating zone technique, we report the first-time successful growth of a DyInO3 sizable crystal, which contains Dy3+-based triangular layers. The fine-tuning of Indium stoichiometry was found to be the key factor in the stabilization of the desired hexagonal phase. The X-ray diffraction study of the crystal structure reveals a non-centrosymmetric P63mc space group. Switchable polarization, i.e., ferroelectricity, and ferroelectric domain configuration are experimentally demonstrated at room temperature. Anisotropic magnetic and thermodynamic measurements unveil antiferromagnetic interactions, the absence of long-range ordering down to 0.1 K, and a possible doublet ground state, indicating a strongly frustrated magnetism. Our findings suggest that the DyInO3 crystal is an excellent platform for studying emergent phenomena and their interplay with coherent topological defects in the quantum realm.
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