Evolution and control of the phase competition morphology in a manganite film

The competition among different phases in perovskite manganites is pronounced since their energies are very close under the interplay of charge, spin, orbital and lattice degrees of freedom. To reveal the roles of underlying interactions, many efforts have been devoted towards directly imaging phase transitions at microscopic scales. Here we show images of the charge-ordered insulator (COI) phase transition from a pure ferromagnetic metal with reducing field or increasing temperature in a strained phase-separated manganite film, using a home-built magnetic force microscope. Compared with the COI melting transition, this reverse transition is sharp, cooperative and martensitic-like with astonishingly unique yet diverse morphologies. The COI domains show variable-dimensional growth at different temperatures and their distribution can illustrate the delicate balance of the underlying interactions in manganites. Our findings also display how phase domain engineering is possible and how the phase competition can be tuned in a controllable manner.Comment: Published versio

Atomic-scale coexistence of short-range magnetic order and superconductivity in Fe1+y_{1+y}Se0.1_{0.1}Te0.9_{0.9}

The ground state of the parent compounds of many high temperature superconductors is an antiferromagnetically (AFM) ordered phase, where superconductivity emerges when the AFM phase transition is suppressed by doping or application of pressure. This behaviour implies a close relation between the two orders. Understanding the interplay between them promises a better understanding of how the superconducting condensate forms from the AFM ordered background. Here we explore this relation in real space at the atomic scale using low temperature spin-polarized scanning tunneling microscopy (SP-STM) and spectroscopy. We investigate the transition from antiferromagnetically ordered $\mathrm{Fe}_{1+y}\mathrm{Te}$ via the spin glass phase in $\mathrm{Fe}_{1+y}\mathrm{Se}_{0.1}\mathrm{Te}_{0.9}$ to superconducting $\mathrm{Fe}_{1+y}\mathrm{Se}_{0.15}\mathrm{Te}_{0.85}$. In $\mathrm{Fe}_{1+y}\mathrm{Se}_{0.1}\mathrm{Te}_{0.9}$ we observe an atomic-scale coexistence of superconductivity and short-ranged bicollinear antiferromagnetic order.Comment: 7 pages, 6 figure

Scanning SQUID-on-tip microscope in a top-loading cryogen-free dilution refrigerator

The scanning superconducting quantum interference device (SQUID) fabricated on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile tool for nanoscale imaging of magnetic, thermal, and transport properties of microscopic devices of quantum materials. We present the design and performance of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight cell mounted at the bottom of the probe and is suspended by springs to suppress vibrations caused by the pulse tube cryocooler. Two capillaries allow in-situ control of helium exchange gas pressure in the cell that is required for thermal imaging. A nanoscale heater is used to create local temperature gradients in the sample, which enables quantitative characterization of the relative vibrations between the tip and the sample. The spectrum of the vibrations shows distinct resonant peaks with maximal power density of about 27 nm/Hz$^{1/2}$ in the in-plane direction. The performance of the SQUID-on-tip microscope is demonstrated by magnetic imaging of the MnBi$_2$Te$_4$ magnetic topological insulator, magnetization and current distribution imaging in a SrRuO$_3$ ferromagnetic oxide thin film, and by thermal imaging of dissipation in graphene.Comment: Submitted to Review of Scientific Instrument

Atomic-scale coexistence of short-range magnetic order and superconductivity in Fe1+ySe0.1Te0.9

Funding: UK EPSRC (EP/I031014/1) (HZ, J-PR, and PW)The ground state of the parent compounds of many high-temperature superconductors is an antiferromagnetically ordered phase, where superconductivity emerges when the antiferromagnetic phase transition is suppressed by doping or application of pressure. This behavior implies a close relation between the two orders. Examining the interplay between them promises a better understanding of how the superconducting condensate forms from the antiferromagnetically ordered background. Here we explore this relation in real space at the atomic scale using low-temperature spin-polarized scanning tunneling microscopy and spectroscopy. We investigate the transition from antiferromagnetically ordered Fe1+yTe via the spin-glass phase in Fe1+ySe0.1Te0.9 to superconducting Fe1+ySe0.15Te0.85. In Fe1+ySe0.1Te0.9 we observe an atomic-scale coexistence of superconductivity and short-ranged bicollinear antiferromagnetic order. However, a direct correlation between the two orders is not observed, supporting the scenario of s± superconducting symmetry in this material. Our work demonstrates a direct probe of the relation between the two orders, which is indispensable for our understanding of high-temperature superconductivity.Publisher PDFPeer reviewe

Roald Dahl Centenary Cardiff Conference

This is a report on the Roald Dahl Centenary Cardiff Conference held in Cardiff, United Kingdom from 16th to 18th June 2016