Searcharxiv⌕ Search

arXiv subjects

Paul C. Canfield

Publications and source records attributed to Paul C. Canfield.

At least 19 recordsLinked to original sources
arXiv2026

Magnetic-Field-Tuned Critical End Point and High-Field Phases in HoMn6Sn6

Topological Kagome RMn6Sn6 materials, where R is a rare-earth, exhibit a rich variety of magnetic phases which provide an opportunity to understand how different spin textures affect topological and transport properties through the application of magnetic field H. In this work, we report experiments on single-crystal HoMn6Sn6, made possible by pulsed magnetic fields of up to 60 T, that permit high-field features of the field-temperature phase diagram to be studied in detail using magnetometry. Complementary, sensitive transport experiments over the same field range employ focused-ion-beam fabrication of novel strain-relieved HoMn6Sn6 devices. In agreement with meanfield calculations, we find a metamagnetic transition at 45 T with H||c between canted phases that ends in a critical end point at about 90 K. As far as we are aware, this is the only critical endpoint that is observed within the RMn6Sn6 kagome metals, and its temperature and field far exceed those of analogous phenomena in other materials. In the low-temperature metamagnetic region, HoMn6Sn6 shows large magnetoresistance, reaching 900 % at 60 T, in concert with Shubnikov de Haas oscillations that suggest a slight Fermi-surface contraction as the metamagnetic transition is crossed. A phase analysis of the oscillations suggests non-trivial band topology, although a firmer attribution must await detailed bandstructure calculations. Near the critical end point, we find deviations from Fermi-liquid behavior in the temperature-dependent magnetoresistance. In the metamagnetic region, the anomalous Hall contribution is not proportional to magnetization, and peaks at about 40 K, suggesting the role of enhanced spin fluctuations near the critical point. At higher temperatures, the anomalous Hall effect reappears at low fields, showing that the magnetization provided by the Ho and Mn sublattices independently affect the conductivity.

cond-mat.mtrl-sci↗
arXiv2026

Peierls Transition and Magnetism in a Dirac Semimetal: CaMnBi$_2$

Dirac semimetals of the form $A$Mn$X_2$ ($A =$ alkaline-earth or divalent rare earth; $X =$ Bi, Sb) host conducting square-net Dirac-electron layers of $X$ atoms interleaved with antiferromagnetic Mn$X$ layers. Hypervalent pnictogen square nets have long been predicted to host an electronically driven Peierls instability, whereas low-temperature anomalies in CaMnBi$_2$ near $T^{*}\sim 50$~K have previously been discussed in terms of possible magnetic canting, TRS breaking, and a resulting Weyl-semimetal (WSM) state. Here we use polarized and unpolarized neutron diffraction, x-ray diffraction, and density functional theory (DFT) to investigate this transition in single-crystal CaMnBi$_2$. We observe a coupled structural/magnetic symmetry-lowering transition at $T^{*}=46(2)$ K from a tetragonal lattice with C-type antiferromagnetism to an orthorhombic phase with unit-cell doubling along the $c$ axis, minimal impact on magnetism, and no measurable uniform spin canting ($\lesssim 2^\circ$). Superlattice peak intensities and the lattice distortion reveal a continuous second-order transition governed by a single primary order parameter. The refined displacement pattern corresponds to a zigzag bond-order-wave (BOW) modulation of in-plane Bi--Bi bonds, providing direct diffraction evidence for a Peierls-type instability of the Dirac-electron Bi layer anticipated by Hoffmann and co-workers [W. Tremel and R. Hoffmann, J. Am. Chem. Soc. 109, 124 (1987); G. A. Papoian and R. Hoffmann, Angew. Chem. Int. Ed. 39, 2408 (2000)]. These results identify the $T^{*}$ anomaly as an intrinsic Dirac-electron-driven Peierls/BOW transition of the Bi square net.

cond-mat.mtrl-sci↗
arXiv2026

Reply to "Comment on 'Topography of Fermi arcs in t-PtBi2 using high-resolution angle-resolved photoemission spectroscopy'"

In a recent work [1] we demonstrated that the Fermi arcs in t-PtBi2 are indeed disconnected segments of the Fermi surface. We showed that the surface state band crosses EF between Weyl points and is has finite band gap at all other momenta until it merges with bulk bands. We did not find evidence of a superconducting gap in the spectra down to 3K. In recent Comment, Sergey Borisenko reanalyzed data from repository posted with our paper and concluded that a superconducting gap with i-wave symmetry is present in our data up to temperatures of 19K. We argue that this claim arises from incorrect identification of the location of Fermi arc and confusion between band gap and superconducting gap. This error was compounded by the fact that Author of the Comment analyzed data from interpolated images used for mapping the Fermi surface that are not suitable for extraction of energy gap on meV scale. This fact was previously communicated to the Author of the Comment during e-mail exchange. We maintain that our conclusion of absence of a superconducting gap above 3 K are valid and consistent with recent STM measurements performed on the same samples, which found surface superconductivity with Tc = 3K, below the temperature at which the data for our ARPES paper was measured.

cond-mat.supr-con↗
arXiv2026

Anisotropic Magnetic and Transport Properties of RAlGe (R = Y, Gd-Tm, Lu)

We grew single crystals of the RAlGe family for R = Y, Gd-Tm, Lu and characterized them with powder X-ray diffraction, temperature dependent specific heat measurements as well as temperature and field dependent resistance and magnetization measurements. These RAlGe materials crystallize in an orthorhombic Cmcm crystal structure in which the R atoms occupy a position with $m$2$m$ point symmetry. We find that when R is a moment bearing rare earth atom, the RAlGe materials order antifferomagnetically at $T_{\text{N}}$ ranging from 5 K (TmAlGe) to 39 K (TbAlGe). A second, lower temperature antiferromagnetic transition is also detected in the range 6-8 K for R = Tb-Ho, but no lower transition is observed (for T above 1.8 K) for R = Er, Tm. The R = Tb-Tm members show evidence for strong crystal field effects influencing the physical properties, where the crystal field favors an easy $a$-axis for R = Tb-Ho and an easy $b$-axis for R = Er, Tm. Of these compounds, strongly uniaxial behavior is observed for DyAlGe and TmAlGe. At T = 2 K, rich metamagnetism is observed when the external field is applied along the $a$-axis for R = Tb--Ho, whereas a single metamagnetic transition is observed (up to 70 kOe) with the field along the $b$-axis when R = Er and Tm. All RAlGe materials show metallic transport behavior and have moderate positive magnetoresistance up to 60-150 % at 2 K superimposed on top of metamagnetic features. The field dependent magnetization measurements on non-moment bearing YAlGe show clear de Haas-van Alphen oscillations, indicating the Fermi surface includes small, high mobility pockets.

cond-mat.mtrl-sci↗
arXiv2026

Fractionation as a Tool to Control Mn/Al Site Mixing and Magnetism in CaMn_{2+x}Al_{10-x}

We report single crystal growth and physical property characterization of CaMn_{2+x}Al_{10-x} crystals grown using a fractionation approach. Three consecutive batches were obtained from the same initial melt composition, systematically sampling neighboring, narrow regions of the ternary Ca-Mn-Al phase diagram. Single-crystal X-ray diffraction measurements reveal Mn/Al site mixing, with the excess Mn concentration, x, decreasing systematically with decreasing decanting temperature. A low-temperature upturn in magnetization and a maximum in electrical resistivity both become progressively weaker with decreasing excess Mn content, suggesting that the previously reported magnetic properties attributed to stoichiometric CaMn_{2}Al_{10} instead arise from an inhomogeneous distribution of excess Mn atoms. More broadly, the results presented in this work demonstrate how fractionation can help distinguish intrinsic magnetic behavior from disorder-induced effects associated with an inhomogeneous distribution of magnetic ions in materials with a finite width of formation, particularly when itinerant magnetism is under consideration.

cond-mat.mtrl-sci↗
arXiv2026

Visualizing impurity-driven scattering phase textures in EuCd2As2

Understanding how disorder modifies electronic states in magnetic semiconductors is important for controlling spin-dependent transport and topological responses. Here we use scanning tunneling microscopy to visualize scattering phase textures in EuCd2As2. By isolating a single surface wavevector we reconstruct spatial phase maps of the local density of states and identify phase dislocations characterized by 2pi winding around impurity sites. These phase singularities emerge systematically within charge puddles generated by Eu interstitials and their positions evolve with bias voltage. We show that their spatial structure is consistent with interference between multiple scattering channels, including contributions from spin-orbit coupling. We provide a model which reproduces phase dislocations and relates the decay of the phase gradient to the relative strength of spin-orbit and scalar scattering. Our results establish a route to access the phase of electronic scattering in real space and study the role of local disorder and spin-orbit interactions in shaping electronic states in quantum materials.

cond-mat.mtrl-sci↗
arXiv2026

Bridging atomic and mesoscopic length scales with Replica Scanning Tunneling Microscopy: Visualizing the atomic lattice of UTe$_2$ and the atomic scale superconducting gap modulations of FeSe close to micron length scales

Scanning Tunneling Microscopy is a cornerstone technique for visualizing the electronic density of states with atomic resolution (typically below 0.1 nm). While the field of view of most STM setups extends up to a few microns, obtaining atomic resolution over these large areas is often impractical and excessively time-consuming. This is due to the need to acquire maps with a point number reaching $10^7$ or more with a full current or conductance vs voltage curve at each point. The standard procedure is to make large scale maps and then select small regions to zoom-in for high-resolution atomic scale analysis. However, this approach fails to address a question which is often critical: Does a specific atomic-scale modulation of the electronic density of states persist over much larger, mesoscopic length scales? Here we present a new method: Replica STM (R-STM), that overcomes this limitation, allowing the study of atomic-scale phenomena up to micron length scales. We obtained new large-area STM tunneling conductance maps in UTe$_2$ and FeSe, spanning areas over 200 nm in size. In these large scale maps we discovered periodic signals with wavelengths significantly exceeding interatomic distances. We show that these large-wavelength periodic signals are replicas of the underlying atomic-scale density of states modulations. R-STM leverages these replica signals to efficiently track atomic-scale features over large areas. We discuss the influence of phase slips, disorder and defects in the replicas. Our results suggest that atomic scale modulations of the superconducting density of states could persist over large length scales in FeSe. R-STM provides a new capability for STM to compare atomic scale with micrometer scale phenomena. The proof of principle of R-STM can be extended to any other scanning probe microscopy experiment where a periodic signal is traced as a function of position.

cond-mat.supr-con↗
arXiv2026

Robust two-dimensional surface superconductivity and vortex lattice in the Weyl semimetal $γ$-PtBi$_2$

The layered compound $γ$-PtBi$_2$ is a topological semimetal with Fermi arcs at the surface joining bulk Weyl points. Recent work has found signatures of surface superconductivity consisting of gap openings compatible with a critical temperature orders of magnitude larger than the bulk value. However, no superconducting vortices have been identified, raising questions about the robustness of the phase coherence. Here we use very low temperature Scanning Tunneling Microscopy (STM) and find robust superconductivity with T$_C=$2.9 K and H$_{C2}\approx$1.8 T linked to the Fermi arcs. We observe quantized superconducting vortices and the Josephson effect, demonstrating two-dimensional macroscopic quantum phase coherence.

cond-mat.supr-con↗
arXiv2026

Room-temperature shape-memory effect in Sr(Ni$_{1-x}$Cu$_x$)$_2$P$_2$

The compound SrNi$_2$P$_2$ can exhibit multiple crystal structures with no P-P pairs bonded (uncollapsed tetragonal, or ucT, state), with one-third of the P-P pairs bonded (one-third collapsed orthorhombic, or tcO, state), or with all P-P pairs bonded (collapsed tetragonal, or cT, state) across the Sr layers. The system can be tuned into its different states by changing temperature, mechanical stress, or chemical composition. Changes in bonding may manifest in changes of macroscopic properties of the material, such as its shape, electrical conductivity, or magnetism. In this work, we show that SrNi$_2$P$_2$ can be tuned among the three states by changing Cu substitution and temperature. We present temperature-dependent resistance and single-crystal x-ray diffraction results in Sr(Ni$_{1-x}$Cu$_x$)$_2$P$_2$ single-crystals that show that Cu substitution favors the P-P bonding, stabilizing the cT state at ambient pressure. We construct a $T-x$ phase diagram that shows how all of these transition temperatures increase with increasing Cu fraction, $x$. The transition between the tcO state and the cT state exhibits a very large thermal hysteresis, which can be tuned to temperatures close to room temperature. In particular, the properties of Sr(Ni$_{0.963}$Cu$_{0.037}$)$_2$P$_2$ may make it suitable for applications as a shape memory material at room temperature.

cond-mat.mtrl-sci↗
arXiv2026

Complex crystal structure prediction using ML-enhanced multi-minima iterative genetic algorithm

Current machine learning (ML) approaches for materials discovery rely heavily on known structural databases, limiting their ability to identify entirely novel structure types. In this work, we develop a multi-minima iterative genetic algorithm (MMIGA) that integrates an artificial-neural-network machine learning (ANN-ML) interatomic potential with an iterative, metadynamics-inspired penalty scheme. We demonstrate the robustness of this method on a complex ternary La-Co-Pb system, characterized by Co-Pb immiscibility and an intricate energy landscape. The ML-enhanced MMIGA successfully predicts the ground-state Pbam structure of the recently synthesized La4Co4Pb antagonistic-pair-phase, a novel structure missed by previous database-reliant ML predictions, while also identifying multiple metastable competing phases. Additionally, we challenged the MMIGA method to predict the structure of La5CoPb2 antagonistic-pair-phase, a new compound discovered during earlier attempts to synthesize the predicted phase La3CoPb. With only knowledge of the composition, our MMIGA approach successfully predicts the orthorhombic structure of La5CoPb2, producing an exact match with the structure independently determined by x-ray diffraction. By efficiently mapping both global minimum and relevant competing metastable states, this approach provides critical theoretical insights into phase selection for novel quantum and magnetic materials.

cond-mat.mtrl-sci↗
arXiv2026

Observation of Flat Bands in Type-II Weyl Semimetal TaRhTe$_{4}$

Flat bands have been theoretically predicted for decades but have only recently been realized in quantum materials such as magic-angle twisted bilayer graphene, kagome and Lieb lattices, and rare-earth metal compounds. To date, only twisted layered materials have enabled tuning of flat-band energies near the electronic chemical potential, thereby influencing transport and thermodynamic properties. Here, we report the presence of flat bands near the chemical potential in bulk TaRhTe$_{4}$, a noncentrosymmetric van-der Waals type-II Weyl semimetal. Flat bands are rarely observed in Weyl semimetals, particularly in nonmagnetic bulk systems, and the observed flat bands were not predicted by density functional theory calculations. TaRhTe$_{4}$ therefore provides a platform in which nontrivial topology coexists with flat bands near the Fermi level, as evidenced by our angle-resolved photoemission spectroscopy measurements.

cond-mat.mtrl-sci↗
arXiv2026

Notes on remanent magnetization measurements in superconductors and hard ferromagnets

Data on zero applied field measurements of remanent magnetization and magnetic relaxation in a BCS superconductor LuNi2B2C and several hard ferromagnets are presented and compared. Apparent similarities and differences, in particular in Thermoremanent Magnetization (TRM) - like, Isothermal Remanent Magnetization (IRM) - like, and remanent magnetization measurements with zigzag temperature sweep measurements are outlined. It is discussed how these results could be relevant for the magnetization measurements in diamond anvil cells.

cond-mat.mtrl-sci↗
arXiv2026

Physical properties of R$_2$Co$_6$Al$_{20-δ}$ (R = Gd-Tm, Y) single crystals

Rare-earth (R) based intermetallic compounds can often exhibit diverse physical properties and distinct magnetic anisotropies. A Notable example are the light rare earth members of the mono-clinic, R$_2$Co$_6$Al$_{19}$ series that are known to display a range of physical properties, from non-Fermi liquid behavior to antiferromagnetic (AFM) ordering, with properties that vary depending on R. In this work, we have extended this series to the heavy rare earths and systematically investigate the synthesis, crystal structure, and physical properties of single crystals of R$_2$Co$_6$Al$_{20-δ}$ for R = Gd - Tm and Y. Single crystal X-ray diffraction reveals that these materials adopt an orthorhombic Imma-type structure with delta varying non-monotonically across the heavy rare earths; ranging from 0.73 for Dy to 0.91 for Gd. Temperature-dependent specific heat, resistivity, and magnetization measurements demonstrate AFM ordering in all materials, with the Neel temperature (TN) ranging from 1.8 K for Ho to 11.8 K for Tb. Notably, Gd and Tb-based materials exhibit two distinct AFM transitions, separated by approximately 2 - 3 K. These findings establish the heavy rare-earth members of the R2Co6Al20-delta series as anisotropic antiferromagnets with strong crystal electric field effects and exchange anisotropy. The observed deviation from de Gennes scaling and the anisotropy crossover across the series highlight the important interplay between RKKY exchange and crystal electric field interactions in this orthorhombic system.

cond-mat.mtrl-sci↗
arXiv2026

Itinerant antiferromagnetism in the antagonistic pair compound Y$_4$Co$_3$Ag

Low dimensional crystallographic motifs have long been associated with desirable physical properties. The confinement of electrons to low dimensions is thought to enhance quantum fluctuations and may promote correlated phenomena. Here, using the antagonistic pair concept, we add Y to the immiscible Co-Ag pair to discover Y$_4$Co$_3$Ag. This compound adopts a monoclinic $I$2/$m$ structure consisting of Y channels that are filled by one-dimensional zigzag and hexagonal Co chains, which extend along the crystallographic $b$-axis with no nearest neighbor contacts between Co and Ag atoms. Transport, magnetic, and specific heat measurements reveal that Y$_4$Co$_3$Ag orders antiferromagnetically at $T_N=14.9$ K with an effective magnetic moment $μ_{\text{eff}}$ = 1.4 $μ_{\text{B}}$/Co. Specific heat measurements show only a small entropy loss on the order of $0.1\,R\ln2$ associated with magnetic order, and magnetization isotherms, in DC fields up to 70 kOe at 1.8 K and in pulsed fields up to 600 kOe at 500 mK, indicate a small ordered moment of less than 0.2 $μ_B$/Co. Taken together, our results imply the presence of small, itinerant moments and strong fluctuations in Y$_4$Co$_3$Ag, suggesting that Y$_4$Co$_3$Ag may be a promising candidate material to investigate itinerant magnetic interactions in a quasi-one dimensional system.

cond-mat.str-el↗
arXiv2026

Ultrafast Magneto-Pressure Spectroscopy and Control of Correlated Phases in a Trilayer Nickelate

Ultrafast spectroscopy under simultaneous high pressure and magnetic field provides a versatile approach for investigating pressure-driven electronic instabilities and correlated phases, and for probing potential bulk superconducting behavior under extreme conditions. However, such an experimental platform has yet to be implemented, standing as a roadblock to a fuller understanding of nonequilibrium superconductivity and vortex-controlled quasi-particle (QP) dynamics. Here, we bridge this capability gap by developing high pressure (up to 40 GPa), high magnetic field (up to 7 T), cryogenic (down to 5 K) femtosecond spectroscopy, and using it to probe magneto-pressure evolution of quasiparticle dynamics in the trilayer nickelate $\mathrm{Pr}_4\mathrm{Ni}_3\mathrm{O}_{10}$. We observe pronounced critical slowing down of QP relaxation at the charge-density-wave transition, which collapses under applied pressure. At higher pressures, the relaxation instead lengthens at low temperature, consistent with incipient superconducting correlations. However, the negligibel magnetic-field-dependence up to 7~T and absence of vortex-induced pre-bottleneck dynamics--robust signatures observed in our controlled bulk superconducting samples--indicates that any superconducting state under the present pressure conditions is likely non-bulk, filamentary, or strongly inhomogeneous. The magneto-pressure ultrafast capability opens a new avenue for resolving outstanding questions surrounding pressure-induced superconductivity and intertwined orders in correlated quantum materials.

cond-mat.supr-con↗
arXiv2026

Growth-Controlled Twinning and Magnetic Anisotropy in CeSb$_2$

Cerium diantimonide (CeSb$_2$) is a layered heavy-fermion Kondo lattice material that hosts complex magnetism and pressure-induced superconductivity. The interpretation of its in-plane anisotropy has remained unsettled due to structural twinning, which superimposes orthogonal magnetic responses. Here we combine controlled crystal growth with magnetization and rotational magnetometry to disentangle the effects of twinning. Nearly untwinned high-quality single crystals reveal the intrinsic in-plane anisotropy: The in-plane easy axis saturates at $M_{\text{easy}}(4~\text{T}) \approx 1.8~μ_{\text{B}}$/Ce, while the in-plane hard axis magnetization is strongly suppressed, nearly linear, and comparable to the out-of-plane response. These results resolve long-standing discrepancies in reported magnetic measurements, in which in-plane metamagnetic transition fields and saturation magnetization varied significantly across previous studies. Growth experiments demonstrate that avoiding the proposed $α$-$β$ structural transition $-$ through Sb-rich flux and slower cooling $-$ systematically reduces twinning. However, powder X-ray diffraction and differential thermal analysis measurements show no clear evidence of a distinct $β$ phase. Our results establish a consistent magnetic phase diagram and provide essential constraints for crystal-electric field models, enabling a clearer understanding of the interplay between anisotropic magnetism and unconventional superconductivity in CeSb$_2$.

cond-mat.str-el↗
arXiv2026

Observation of Iso-Symmetric Structural and Lifshitz Transitions in Quasi-one-dimensional CrNbSe$_5$

Chalcogenides-rich transition metal compounds host a rich landscape of emergent quantum phenomena that are intimately governed by their quasi-one-dimensional chemical-bonding frameworks and their response to external perturbations such as pressure. Here, we report a pressure-induced iso-symmetric structural transition in the quasi-one-dimensional compound CrNbSe$_5$, in which the electronic ground state is controlled not by symmetry breaking but by a continuous reorganization of local bonding interactions. Applied pressure reversibly tunes CrNbSe$_5$ between semiconducting and semimetallic states, enabling access to low- and high-carrier electronic regimes through direct modulation of metal-chalcogen bonding. High-pressure single-crystal X-ray diffraction directly resolves the evolution of Cr-Se and Nb-Se bond distances, coordination polyhedra, and connectivity, revealing a fully reversible semimetal-semiconductor-semimetal transition driven by gradual yet cooperative bond rearrangements within a preserved crystallographic symmetry. In contrast to chemical substitution, which irreversibly alters composition and introduces disorder, pressure acts as a clean, continuous control parameter that reshapes the bonding landscape without disrupting structural symmetry. These results establish CrNbSe$_5$ as a model system for electronically driven phase switching via tunable chemical bonding, highlighting iso-symmetric bond reorganization as a powerful design principle for pressure-controlled electronic and spintronic functionalities.

cond-mat.mtrl-sci↗
arXiv2026

Direct observation of vortex liquid droplets in the iron pnictide superconductor CaKAs$_4$Fe$_4$ at $0.5T$_c$

Type-II superconductors under magnetic fields are in a quantum coherent non-dissipative state as long as vortices remain pinned. Dissipation appears when vortices depin, eventually driven by thermal fluctuations. This can be associated to a melting transition between a vortex solid and a vortex liquid. This transition is almost always observed very close to T$_c$ when probed by macroscopic experiments. However, it remains unclear how the vortex solid responds to thermal fluctuations at the scale of individual vortices far from the melting transition. Here we use scanning tunneling microscopy (STM) to visualize vortices in CaKAs$_4$Fe$_4$ (T$_c \approx$ 35 K). We find vortex liquid droplets-localized regions in space where vortices strongly fluctuate due to thermal exctiation-at temperatures as low as 0.5\,T$_c$. Our results show that the onset of dissipation at the local scale occurs at temperatures considerably below T$_c$ in type-II superconductors.

cond-mat.supr-con↗