npj Quantum Materials

Journal: npj Quantum Materials

Abbreviation

npj Quantum Mater.

Publisher

Nature

ISSN

2397-4648

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Publications 1 - 10 of 22

Nodal-To-nodeless superconducting order parameter in LaFeAs1-xPxO synthesized under high pressure
Shiroka, Toni; Barbero, Nicolò; Khasanov, Rustem; et al. (2018)
npj Quantum Materials
Similar to chemical doping, pressure produces and stabilizes new phases of known materials, whose properties may differ greatly from those of their standard counterparts. Here, by considering a series of LaFeAs1−xP x O iron-pnictides synthesized under high-pressure high-temperature conditions, we investigate the simultaneous effects of pressure and isoelectronic doping in the 1111 family. Results of numerous macroscopic and microscopic technique measurements unambiguously show a radically different phase diagram for the pressure-grown materials, characterized by the lack of magnetic order and the persistence of superconductivity across the whole 0.3 ≤ x ≤ 0.7 doping range. This unexpected scenario is accompanied by a branching in the electronic properties across x = 0.5, involving both the normal and superconducting phases. Most notably, the superconducting order parameter evolves from nodal (for x < 0.5) to nodeless (for x ≥ 0.5), in clear contrast to other 1111 and 122 iron-based materials grown under ambient-pressure conditions.
Perspective: an X-ray view of the coherent driving of materials
Johnson, Steven; Staub, Urs (2025)
npj Quantum Materials
We discuss new opportunities in the study of materials arising from combining high intensity, phase-stable light pulses in the THz and mid-infrared with current and upcoming instrumentation at X-ray free electron laser (XFEL) facilities. We briefly summarize the relevant new technologies involved in making long-wavelength pump pulses, and upcoming advances in XFEL instrumentation. We also describe some initial key experiments in this quickly developing field, and provide an outlook.
Re1−xMox as an ideal test case of time-reversal symmetry breaking in unconventional superconductors
Shang, Tian; Baines, Christopher; Chang, Lieh-Jeng; et al. (2020)
npj Quantum Materials
Non-centrosymmetric superconductors (NCSCs) are promising candidates in the search for unconventional and topological superconductivity. The α-Mn-type rhenium-based alloys represent excellent examples of NCSCs, where spontaneous magnetic fields, peculiar to time-reversal symmetry (TRS) breaking, have been shown to develop in the superconducting phase. By converse, TRS is preserved in many other isostructural NCSCs, thus leaving the key question about its origin fully open. Here, we consider the superconducting Re1−xMox (0 ≤ x ≤ 1) family, which comprises both centro- and non-centrosymmetric structures and includes also two extra superconducting phases, β-CrFe and bcc-W. Muon-spin relaxation and rotation (μSR) measurements show a gradual increase of the relaxation rate below Tc, yet its independence of the crystal structure, suggesting that rhenium presence and its amount are among the key factors for the appearance and the extent of TRS breaking in the α-Mn-type NCSCs. The reported results propose Re1−xMox as an ideal test case for investigating TRS breaking in unconventional superconductors.
Local electric-field control of multiferroic spin-spiral domains in TbMnO3
Schönherr, Peggy; Manz, Sebastian; Kürten, Lukas; et al. (2020)
npj Quantum Materials
Spin-spiral multiferroics exhibit a magnetoelectric coupling effects, leading to the formation of hybrid domains with inseparably entangled ferroelectric and antiferromagnetic order parameters. Due to this strong magnetoelectric coupling, conceptually advanced ways for controlling antiferromagnetism become possible and it has been reported that electric fields and laser pulses can reversibly switch the antiferromagnetic order. This switching of antiferromagnetic spin textures is of great interest for the emergent field of antiferromagnetic spintronics. Established approaches, however, require either high voltages or intense laser fields and are currently limited to the micrometer length scale, which forfeits the technological merit. Here, we image and control hybrid multiferroic domains in the spin-spiral system TbMnO3 using low-temperature electrostatic force microscopy (EFM). First, we show that image generation in EFM happens via surface screening charges, which allows for probing the previously hidden magnetically induced ferroelectric order in TbMnO3 (PS = 6 × 10−4 C/m2). We then set the antiferromagnetic domain configuration by acting on the surface screening charges with the EFM probe tip. Our study enables detection of entangled ferroelectric and antiferromagnetic domains with high sensitivity. The spatial resolution is limited only by the physical size of the probe tip, introducing a pathway towards controlling antiferromagnetic order at the nanoscale and with low energy.
Wannier states and spin supersolid physics in the triangular antiferromagnet K₂Co(SeO₃)₂
Zhu, Mengze; Chinellato, Leandro M.; Romerio, Viola; et al. (2025)
npj Quantum Materials
We combine ultra-high-resolution inelastic neutron scattering and quantum Monte Carlo simulations to study thermodynamics and spin excitations in the spin-supersolid phase of the triangular lattice XXZ antiferromagnet K₂Co(SeO₃)₂ under zero and non-zero magnetic field. BKT transitions signaling the onset of Ising and supersolid order are clearly identified, and the Wannier entropy is experimentally recovered just above the supersolid phase. At low temperatures, with an experimental resolution of about 23 μeV, no discrete coherent magnon modes are resolved within a broad scattering continuum. Alongside gapless excitations, a pseudo-Goldstone mode with a 0.06 meV gap is observed. A second, higher-energy continuum replaces single-spin-flip excitations of the Ising model. Under applied fields, the continuum evolves into coherent spin waves, with Goldstone and pseudo-Goldstone sectors responding differently. The experiments and simulations show excellent quantitative agreement.
Charge dynamics of a noncentrosymmetric magnetic Weyl semimetal
Yang, R.; Corasaniti, Matteo; Le, Cong-Cong; et al. (2022)
npj Quantum Materials
The interplay of topology with magnetism in Weyl semimetals recently arose to a vanguard topic, because of novel physical scenarios with anomalous transport properties. Here, we address the charge dynamics of the noncentrosymmetric and ferromagnetic (T-C similar to 15 K) PrAlGe material and discover that it harbours electronic correlations, which are reflected in a sizeable reduction of the Fermi velocity with respect to the bare band value at low temperatures (T). At T < T-C, the optical response registers a band reconstruction, which additionally causes a reshuffling of spectral weight, pertinent to the electronic environment of the type-I Weyl fermions and tracing the remarkable anomalous Hall conductivity (AHC). With the support of first-principles calculations, we provide evidence for the intimate relationship between a topological resonance of the absorption spectrum and the progressively enhanced occupation of non-trivial states with large Berry curvatures, a requirement for AHC.
Microscopic evidence for anisotropic multigap superconductivity in the CsV3Sb5 kagome superconductor
Gupta, Ritu; Das, Debarchan; Mielke, Charles Hillis, III; et al. (2022)
npj Quantum Materials
The recently discovered kagome superconductor CsV3Sb5 (T-c similar or equal to 2.5 K) has been found to host charge order as well as a non-trivial band topology, encompassing multiple Dirac points and probable surface states. Such a complex and phenomenologically rich system is, therefore, an ideal playground for observing unusual electronic phases. Here, we report anisotropic superconducting properties of CsV3Sb5 by means of transverse-field muon spin rotation (mu SR) experiments. The fits of temperature dependences of in-plane and out-of-plane components of the magnetic penetration depth suggest that the superconducting order parameter may have a two-gap (s + s)-wave symmetry. The multiband nature of superconductivity could be further supported by the different temperature dependences of the anisotropic magnetic penetration depth gamma lambda(T) and upper critical field Y-Bc2(T). The relaxation rates obtained from zero field mu SR experiments do not show noticeable change across the superconducting transition, indicating that superconductivity does not break time reversal symmetry.
Orbital structure of the effective pairing interaction in the high-temperature superconducting cuprates
Mai, Peizhi; Balduzzi, Giovanni; Johnston, Steven; et al. (2021)
npj Quantum Materials
The nature of the effective interaction responsible for pairing in the high-temperature superconducting cuprates remains unsettled. This question has been studied extensively using the simplified single-band Hubbard model, which does not explicitly consider the orbital degrees of freedom of the relevant CuO2 planes. Here, we use a dynamical cluster quantum Monte Carlo approximation to study the orbital structure of the pairing interaction in the three-band Hubbard model, which treats the orbital degrees of freedom explicitly. We find that the interaction predominately acts between neighboring copper orbitals, but with significant additional weight appearing on the surrounding bonding molecular oxygen orbitals. By explicitly comparing these results to those from the simpler single-band Hubbard model, our study provides strong support for the single-band framework for describing superconductivity in the cuprates.
Field-induced double spin spiral in a frustrated chiral magnet
Ramakrishnan, Mahesh; Constable, Evan; Cano, Andres; et al. (2019)
npj Quantum Materials
Magnetic ground states with peculiar spin textures, such as magnetic skyrmions and multifunctional domains are of enormous interest for the fundamental physics governing their origin as well as potential applications in emerging technologies. Of particular interest are multiferroics, where sophisticated interactions between electric and magnetic phenomena can be used to tailor several functionalities. We report the direct observation of a magnetic field induced long-wavelength spin spiral modulation in the chiral compound Ba3TaFe3Si2O14, which emerges out of a helical ground state, and is hallmarked by the onset of a unique chirality-dependent contribution to the bulk electric polarization. The periodicity of the field-induced modulation, several hundreds of nm depending on the field value, is comparable to the length scales of mesoscopic topological defects such as skyrmions, merons, and solitons. The phase transition and observed threshold behavior are consistent with a phenomenology based on the allowed Lifshitz invariants for the chiral symmetry of langasite, which intriguingly contain all the essential ingredients for the realization of topologically stable antiferromagnetic skyrmions. Our findings open up new directions to explore topological correlations of antiferromagnetic spintronic systems based on non-collinear magnetic systems with additional ferroic functionalities.
Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3
Moll, Philip J.W.; Helm, Toni; Zhang, Shang-Shun; et al. (2017)
npj Quantum Materials
Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. The cubic system CeIn3 has attracted significant attention as a structurally isotropic Kondo lattice material possessing the minimum required complexity to still reveal this rich physics. By using magnetic fields with strengths comparable to the crystal field energy scale, we illustrate a strong field-induced anisotropy as a consequence of non-spherically symmetric spin interactions in the prototypical heavy fermion material CeIn3. This work demonstrates the importance of magnetic anisotropy in modeling f-electron materials when the orbital character of the 4f wavefunction changes (e.g., with pressure or composition). In addition, magnetic fields are shown to tune the effective hybridization and exchange interactions potentially leading to new exotic field tuned effects in f-based materials.

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