Yubin Hou

Giant magnetodielectric effect in Terfenol-D/PZT magnetoelectric laminate composite

The magnetic field dependence of the dielectric permittivity of Terfenol-D/PbZr(x)Ti(1-x)O(3) magnetoelectric composites in the temperature range from 200 K to 340 K was investigated systematically. It was found that there is a large magnetodielectric effect up to 15% around the electromechanical resonance frequency in a magnetic field of 5 kOe at room temperature. Nonmonotonic variations of dielectric permittivity with magnetic fields are associated with the mechanical energy loss due to magnetic domain wall motion in the magnetostrictive layer Terfenol-D. A numerical modeling is proposed and agrees well with the experimental data. The results are of significance in the development of magnetic-field-tuned electronic devices at room temperature

Self-manifestation and universal correction of image distortion in scanning tunneling microscopy with spiral scan

We demonstrate that severe distortions may occur but hard to identify in a standard line-by-line scanned scanning tunneling microscope image, deforming the atomic lattice into a completely different structure type and leading to a wrong interpretation of the data. We also show that a spiral scan image can reveal the details of the drifting by causing the atomic rows to bend with the curvatures being closely related to the extent and direction of the drifting. By straightening the curved atomic rows, the true atomic arrangement can thus be precisely recovered.

Note: A compact, rigid, and easy-to-build piezo motor: The intact-tube GeckoDrive

We report an extremely simple, rigid, low machine tolerance, yet high performance piezoelectric motor, in which two rings are coaxially glued at the ends of one intact piezotube, respectively, using the proper gluing method. A central shaft is pushed to press against the inner edges of the rings by a spring strip at a proper axial position and in the gap between the shaft and the inner wall of the piezotube. It is compared with other important forms of three-friction driven motors and shows advantageous structure and unexpectedly excellent performance, hence deserving a new name: the GeckoDrive.

A high-stability scanning tunneling microscope achieved by an isolated tiny scanner with low voltage imaging capability

We present a novel homebuilt scanning tunneling microscope (STM) with high quality atomic resolution. It is equipped with a small but powerful GeckoDrive piezoelectric motor which drives a miniature and detachable scanning part to implement coarse approach. The scanning part is a tiny piezoelectric tube scanner (industry type: PZT-8, whose d31 coefficient is one of the lowest) housed in a slightly bigger polished sapphire tube, which is riding on and spring clamped against the knife edges of a tungsten slot. The STM so constructed shows low back-lashing and drifting and high repeatability and immunity to external vibrations. These are confirmed by its low imaging voltages, low distortions in the spiral scanned images, and high atomic resolution quality even when the STM is placed on the ground of the fifth floor without any external or internal vibration isolation devices.

Moderate and strong static magnetic fields directly affect EGFR kinase domain orientation to inhibit cancer cell proliferation.

Static magnetic fields (SMFs) can affect cell proliferation in a cell-type and intensity-dependent way but the mechanism remains unclear. At the same time, although the diamagnetic anisotropy of proteins has been proposed decades ago, the behavior of isolated proteins in magnetic fields has not been directly observed. Here we show that SMFs can affect isolated proteins at the single molecular level in an intensity-dependent manner. We found that Epidermal Growth Factor Receptor (EGFR), a protein that is overexpressed and highly activated in multiple cancers, can be directly inhibited by SMFs. Using Liquid-phase Scanning Tunneling Microscopy (STM) to examine pure EGFR kinase domain proteins at the single molecule level in solution, we observed orientation changes of these proteins in response to SMFs. This may interrupt inter-molecular interactions between EGFR monomers, which are critical for their activation. In molecular dynamics (MD) simulations, 1-9T SMFs caused increased probability of EGFR in parallel with the magnetic field direction in an intensity-dependent manner. A superconducting ultrastrong 9T magnet reduced proliferation of CHO-EGFR cells (Chinese Hamster Ovary cells with EGFR overexpression) and EGFR-expressing cancer cell lines by ~35%, but minimally affected CHO cells. We predict that similar effects of magnetic fields can also be applied to some other proteins such as ion channels. Our paper will help clarify some dilemmas in this field and encourage further investigations in order to achieve a better understanding of the biological effects of SMFs.

Forward and backward diodelike rectifying properties of the heterojunctions composed of La1−xSrxCoO3−δ and 0.7wt% Nb-doped SrTiO3

Heterojunctions composed of La1-xSrxCoO3-delta (x= 0.4 and 0.5) and 0.7 wt % Nb- doped SrTiO3 were fabricated and exhibited good rectifying properties. The asymmetric current- voltage relations for the x=0.4 and x=0.5 junctions display opposite shapes: the former has a forward shape, while the latter shows a backward one. The x=0.4 junction can be viewed as a Schottky diode. For the x=0.5 junction, the forward bias currents show much less temperature dependence than the reverse ones and the reverse voltage V-char, at which the bias current is 10 mu A, displays a distinct change at the ferromagnetic transition temperature of the cobalt oxide of the junction. These observations in the x=0.5 junction can be understood by a nearly degenerate model together with its temperature- dependent magnetism

A compact high field magnetic force microscope

We present the design and performance of a simple and compact magnetic force microscope (MFM), whose tip-sample coarse approach is implemented by the piezoelectric tube scanner (PTS) itself. In brief, a square rod shaft is axially spring-clamped on the inner wall of a metal tube which is glued inside the free end of the PTS. The shaft can thus be driven by the PTS to realize image scan and inertial stepping coarse approach. To enhance the inertial force, each of the four outer electrodes of the PTS is driven by an independent port of the controller. The MFM scan head is so compact that it can easily fit into the 52mm low temperature bore of a 20T superconducting magnet. The performance of the MFM is demonstrated by imaging a manganite thin film at low temperature and in magnetic fields up to 15T.

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.

18/20 T high magnetic field scanning tunneling microscope with fully low voltage operability, high current resolution, and large scale searching ability

We present a home-built 18/20 T high magnetic field scanning tunneling microscope (STM) featuring fully low voltage (lower than ±15 V) operability in low temperatures, large scale searching ability, and 20 fA high current resolution (measured by using a 100 GOhm dummy resistor to replace the tip-sample junction) with a bandwidth of 3.03 kHz. To accomplish low voltage operation which is important in achieving high precision, low noise, and low interference with the strong magnetic field, the coarse approach is implemented with an inertial slider driven by the lateral bending of a piezoelectric scanner tube (PST) whose inner electrode is axially split into two for enhanced bending per volt. The PST can also drive the same sliding piece to inertial slide in the other bending direction (along the sample surface) of the PST, which realizes the large area searching ability. The STM head is housed in a three segment tubular chamber, which is detachable near the STM head for the convenience of sample and tip changes. Atomic resolution images of a graphite sample taken under 17.6 T and 18.0001 T are presented to show its performance.

Quantum Percolation and Magnetic Nanodroplet States in Electronically Phase-Separated Manganite Nanowires

One-dimensional (1D) confinement has been revealed to effectively tune the properties of materials in homogeneous states. The 1D physics can be further enriched by electronic inhomogeneity, which unfortunately remains largely unknown. Here we demonstrate the ultrahigh sensitivity to magnetic fluctuations and the tunability of phase stability in the electronic transport properties of self-assembled electronically phase-separated manganite nanowires with extreme aspect ratio. The onset of magnetic nanodroplet state, a precursor to the ferromagnetic metallic state, is unambiguously revealed, which is attributed to the small lateral size of the nanowires that is comparable to the droplet size. Moreover, the quasi-1D anisotropy stabilizes thin insulating domains to form intrinsic tunneling junctions in the low temperature range, which is robust even under magnetic field up to 14 T and thus essentially modifies the classic 1D percolation picture to stabilize a novel quantum percolation state. A new phase diagram is therefore established for the manganite system under quasi-1D confinement for the first time. Our findings offer new insight into understanding and manipulating the colorful properties of the electronically phase-separated systems via dimensionality engineering.