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Junqiang Zhang

Publications and source records attributed to Junqiang Zhang.

13 recordsLinked to original sources
arXiv2026

Spatiotemporal programming via asymmetric dielectric engineering for nonvolatile 2D optoelectronics

Ambipolar two dimensional (2D) semiconductors integrated with floating-gate architectures offer a promising platform for nonvolatile, reconfigurable electronics. However, the switching between p-n and n-p junction polarities has conventionally required complex multi-gate designs, hindering the scalability and integration density. Here, we demonstrate a spatiotemporal programming strategy using a dual-floating-gate architecture with a symmetry broken tunneling dielectric. An asymmetric dielectric stack creates distinct tunneling thresholds for two floating gates, enabling a single input gate to encode spatial doping profiles in the 2D channel via defined voltage pulse sequences. We achieve on demand, nonvolatile, and reversible switching between p-n and n-p configurations with excellent retention and endurance. The reconfigurable homojunction serves as a multifunctional platform for logic encoding, rectification, photodetection, and in sensor computing. This work establishes a design paradigm that replaces spatial input complexity with spatiotemporal programming, paving the way for high-density, multifunctional intelligent hardware.

cond-mat.mes-hall↗
arXiv2025

Angle-dependent resonant tunneling and thermoelectric energy management in a hybrid 1D-2D-1D semiconductor nanostructure

Low-dimensional semiconductors have been widely exploited in thermoelectric energy conversion for high efficiencies due to their suppressed lattice thermal conduction, sharply defined electronic density of states, and tunable energy-selective electron transmission. However, the widespread challenge of Fermi-level pinning or doping constraints limit precise control over thermoelectric energy management via chemical potential modulation. Here, we proposed an alternative strategy: leveraging angle-dependent electron incidence to dynamically manipulate electron transmission and heat transport, which was implemented theoretically in a two-dimensional InP/InAs/InP double-barrier heterostructure integrated with laterally one-dimensional electrodes. By combining the transfer matrix method and Landauer formalism, we demonstrated the angle-dependent resonant tunneling dynamics, tunable negative differential resistance effect, and near-Carnot limits in thermoelectric energy conversions. Angular modulation enables precise control over transmission resonances, facilitating dynamic transitions among thermoelectric regimes (power generation, cooling, and hybrid heating) without requiring extreme chemical potential shifts. This work establishes angularly resolved electron transmission as a versatile mechanism for on-chip thermal management and cryogenic applications, offering a pathway to circumvent material limitations in next-generation nanoelectronics and quantum devices.

cond-mat.mes-hall↗
arXiv2024

Measures supported on partly normal numbers

A real number $x$ is normal with respect to an integer base $b \geq 2$ if its digit expansion in this base is ``equitable'', in the sense that for $k \geq 1$, every ordered sequence of $k$ digits from $\{0, 1, \ldots, b-1\}$ occurs in the digit expansion of $x$ with the same limiting frequency. Borel's classical result \cite{b09} asserts that Lebesgue-almost every number $x$ is normal in every base $b \geq 2$. This three-part article considers sets of partial normality. Given any choice of integer bases $\mathscr{B}, \mathscr{B}' \subseteq \{2, 3, \ldots\}$, we investigate measure-theoretic properties of the set $\mathscr{N}(\mathscr{B}, \mathscr{B}')$, whose members are, by definition, normal in the bases of $\mathscr{B}$ and non-normal in the bases of $\mathscr{B}'$. A pair of sets $(\mathscr{B}, \mathscr{B}')$ is compatible if any $(b, b') \in \mathscr{B} \times \mathscr{B}'$ is multiplicatively independent. For compatible $(\mathscr{B}, \mathscr{B}')$ with $\mathscr{B}' \ne \emptyset$, we construct singular probability measures supported on $\mathscr N(\mathscr{B}, \mathscr{B}')$ that are both Frostman and Rajchman, extending prior work of Pollington \cite{p81} and Lyons \cite{l86}. The Rajchman property completely answers a question of Kahane and Salem \cite{Kahane-Salem-64}, identifying $\mathscr N(\mathscr{B}, \mathscr{B}')$ as a set of multiplicity (in the Fourier-analytic sense) if and only if $(\mathscr{B}, \mathscr{B}')$ is compatible. The methodological contribution of the article is the construction of a class of probability measures called skewed measures. These measures depend on a number of parameters that can be independently adjusted to ensure (subsets of) properties such as almost everywhere normality, non-normality, ball conditions and Fourier decay.

math.CA↗
arXiv2024

On odd-normal numbers

A real number $x$ is considered normal in an integer base $b \geq 2$ if its digit expansion in this base is ``equitable'', ensuring that for each $k \geq 1$, every ordered sequence of $k$ digits from $\{0, 1, \ldots, b-1\}$ occurs in the digit expansion of $x$ with the same limiting frequency. Borel's classical result \cite{b09} asserts that Lebesgue-almost every $x \in \mathbb R$ is normal in every base $b \geq 2$. This paper serves as a case study of the measure-theoretic properties of Lebesgue-null sets containing numbers that are normal only in certain bases. We consider the set $\mathscr N(\mathscr{O}, \mathscr{E})$ of reals that are normal in odd bases but not in even ones. This set has full Hausdorff dimension \cite{p81} but zero Fourier dimension. The latter condition means that $\mathscr N(\mathscr{O}, \mathscr{E})$ cannot support a probability measure whose Fourier transform has power decay at infinity. Our main result is that $\mathscr N(\mathscr{O}, \mathscr{E})$ supports a Rajchman measure $μ$, whose Fourier transform $\widehatμ(ξ)$ approaches 0 as $|ξ| \rightarrow \infty$ by definiton, albeit slower than any negative power of $|ξ|$. Moreover, the decay rate of $\widehatμ$ is essentially optimal, subject to the constraints of its support. The methods draw inspiration from the number-theoretic results of Schmidt \cite{s60} and a construction of Lyons \cite{l86}. As a consequence, $\mathscr N(\mathscr{O}, \mathscr{E})$ emerges as a set of multiplicity, in the sense of Fourier analysis. This addresses a question posed by Kahane and Salem \cite{Kahane-Salem-64} in the special case of $\mathscr N(\mathscr{O}, \mathscr{E})$.

math.CA↗
arXiv2019

Quantitative Boundedness of Littlewood--Paley Functions on Weighted Lebesgue Spaces in the Schrödinger Setting

Let $L:=-Δ+V$ be the Schrödinger operator on $\mathbb{R}^n$ with $n\geq 3$, where $V$ is a non-negative potential which belongs to certain reverse Hölder class $RH_q(\mathbb{R}^n)$ with $q\in (n/2,\,\infty)$. In this article, the authors obtain the quantitative weighted boundedness of Littlewood--Paley functions $g_L$, $S_L$ and $g_{L,\,λ}^\ast$, associated to $L$, on weighted Lebesgue spaces $L^p(w)$, where $w$ belongs to the class of Muckenhoupt $A_p$ weights adapted to $L$.

math.CA↗
arXiv2018

Atomic Characterizations of Hardy Spaces Associated to Schrödinger Type Operators

In this article, the authors consider the Schrödinger type operator $L:=-{\rm div}(A\nabla)+V$ on $\mathbb{R}^n$ with $n\geq 3$, where the matrix $A$ is symmetric and satisfies uniformly elliptic condition and the nonnegative potential $V$ belongs to the reverse Hölder class $RH_q(\mathbb{R}^n)$ with $q\in(n/2,\,\infty)$. Let $p(\cdot):\ \mathbb{R}^n\to(0,\,1]$ be a variable exponent function satisfying the globally $\log$-Hölder continuous condition. The authors introduce the variable Hardy space $H_L^{p(\cdot)}(\mathbb{R}^n)$ associated to $L$ and establish its atomic characterization. The atoms here are closer to the atoms of variable Hardy space $H^{p(\cdot)}(\mathbb{R}^n)$ in spirit, which further implies that $H^{p(\cdot)}(\mathbb{R}^n)$ is continuously embedded in $H_L^{p(\cdot)}(\mathbb{R}^n)$.

math.CA↗
arXiv2018

Some Estimates of Schrödinger Type Operators on Variable Lebesgue and Hardy Spaces

In this article, the authors consider the Schrödinger type operator $L:=-{\rm div}(A\nabla)+V$ on $\mathbb{R}^n$ with $n\geq 3$, where the matrix $A$ satisfies uniformly elliptic condition and the nonnegative potential $V$ belongs to the reverse Hölder class $RH_q(\mathbb{R}^n)$ with $q\in(n/2,\,\infty)$. Let $p(\cdot):\ \mathbb{R}^n\to(0,\,\infty)$ be a variable exponent function satisfying the globally $\log$-Hölder continuous condition. When $p(\cdot):\ \mathbb{R}^n\to(1,\,\infty)$, the authors prove that the operators $VL^{-1}$, $V^{1/2}\nabla L^{-1}$ and $\nabla^2L^{-1}$ are bounded on variable Lebesgue space $L^{p(\cdot)}(\mathbb{R}^n)$. When $p(\cdot):\ \mathbb{R}^n\to(0,\,1]$, the authors introduce the variable Hardy space $H_L^{p(\cdot)}(\mathbb{R}^n)$, associated to $L$, and show that $VL^{-1}$, $V^{1/2}\nabla L^{-1}$ and $\nabla^2L^{-1}$ are bounded from $H_L^{p(\cdot)}(\mathbb{R}^n)$ to $L^{p(\cdot)}(\mathbb{R}^n)$.

math.CA↗
arXiv2017

Variable Hardy Spaces Associated with Operators Satisfying Davies-Gaffney Estimates

Let $L$ be a one-to-one operator of type $ω$ in $L^2(\mathbb{R}^n)$, with $ω\in[0,\,π/2)$, which has a bounded holomorphic functional calculus and satisfies the Davies-Gaffney estimates. Let $p(\cdot):\ \mathbb{R}^n\to(0,\,1]$ be a variable exponent function satisfying the globally log-Hölder continuous condition. In this article, the authors introduce the variable Hardy space $H^{p(\cdot)}_L(\mathbb{R}^n)$ associated with $L$. By means of variable tent spaces, the authors establish the molecular characterization of $H^{p(\cdot)}_L(\mathbb{R}^n)$. Then the authors show that the dual space of $H^{p(\cdot)}_L(\mathbb{R}^n)$ is the BMO-type space ${\rm BMO}_{p(\cdot),\,L^\ast}(\mathbb{R}^n)$, where $L^\ast$ denotes the adjoint operator of $L$. In particular, when $L$ is the second order divergence form elliptic operator with complex bounded measurable coefficients, the authors obtain the non-tangential maximal function characterization of $H^{p(\cdot)}_L(\mathbb{R}^n)$ and show that the fractional integral $L^{-α}$ for $α\in(0,\,\frac12]$ is bounded from $H_L^{p(\cdot)}(\mathbb{R}^n)$ to $H_L^{q(\cdot)}(\mathbb{R}^n)$ with $\frac1{p(\cdot)}-\frac1{q(\cdot)}=\frac{2α}{n}$ and the Riesz transform $\nabla L^{-1/2}$ is bounded from $H^{p(\cdot)}_L(\mathbb{R}^n)$ to the variable Hardy space $H^{p(\cdot)}(\mathbb{R}^n)$.

math.CA↗
arXiv2015

Weighted $L^p$ Estimates of Kato Square Roots Associated to Degenerate Elliptic Operators

Let $w$ be a Muckenhoupt $A_2(\mathbb{R}^n)$ weight and $L_w:=-w^{-1}\mathop\mathrm{div}(A\nabla)$ the degenerate elliptic operator on the Euclidean space $\mathbb{R}^n$, $n\geq 2$. In this article, the authors establish some weighted $L^p$ estimates of Kato square roots associated to the degenerate elliptic operators $L_w$. More precisely, the authors prove that, for $w\in A_{p}(\mathbb{R}^n)$, $p\in(\frac{2n}{n+1},\,2]$ and any $f\in C^\infty_c(\mathbb{R}^n)$, $\|L_w^{1/2}(f)\|_{L^p(w,\,\mathbb{R}^n)}\sim \|\nabla f\|_{L^p(w,\,\mathbb{R}^n)}$, where $C_c^\infty(\mathbb{R}^n)$ denotes the set of all infinitely differential functions with compact supports.

math.CA↗
arXiv2015

Riesz Transform Characterizations of Hardy Spaces Associated to Degenerate Elliptic Operators

Let $w$ be a Muckenhoupt $A_2(\mathbb{R}^n)$ weight and $L_w:=-w^{-1}\mathop\mathrm{div}(A\nabla)$ the degenerate elliptic operator on the Euclidean space $\mathbb{R}^n$. In this article, the authors establish the Riesz transform characterization of the Hardy space $H_{L_w}^p(\mathbb{R}^n)$ associated with $L_w$, for $w\in A_{q}(\mathbb{R}^n)$ and $w^{-1}\in A_{2-\frac{2}{n}}(\mathbb{R}^n)$ with $n\geq 3$, $q\in[1,2]$ and $p\in(q(\frac{1}{r}+\frac{q-1}{2}+\frac{1}{n})^{-1},1]$ if, for some $r\in[1,\,2)$, $\{tL_w e^{-tL_w}\}_{t\geq 0}$ satisfies the weighted $L^r-L^2$ full off-diagonal estimate.

math.CA↗
arXiv2014

Experimental demonstration of longitudinal beam phase space linearizer in a free-electron laser facility by corrugated structures

Removal of residual linear energy chirp and intrinsic nonlinear energy curvature in the relativistic electron beam from radiofrequency linear accelerator is of paramount importance for efficient lasing of a high-gain free-electron laser. Recently, it was theoretically and experimentally demonstrated that the longitudinal wakefield excited by the electrons itself in the corrugated structure allows for precise control of the electron beam phase space. In this Letter, we report the first utilization of a corrugated structure as beam linearizer in the operation of a seeded free-electron laser driven by a 140 MeV linear accelerator, where a gain of ~10,000 over spontaneous emission was achieved at the second harmonic of the 1047 nm seed laser, and a free-electron laser bandwidth narrowing by about 50% was observed, in good agreement with the theoretical expectations.

physics.acc-ph↗
arXiv2013

Boundedness of Intrinsic Littlewood-Paley Functions on Musielak-Orlicz Morrey and Campanato Spaces

Let $φ: {\mathbb R^n}\times [0,\infty)\to[0,\infty)$ be such that $\vz(x,\cdot)$ is nondecreasing, $φ(x,0)=0$, $φ(x,t)>0$ when $t>0$, $\lim_{t\to\infty}φ(x,t)=\infty$ and $\vz(\cdot,t)$ is a Muckenhoupt $A_\infty({\mathbb R^n})$ weight uniformly in $t$. Let $ϕ: [0,\infty)\to[0,\infty)$ be nondecreasing. In this article, the authors introduce the Musielak-Orlicz Morrey space $\mathcal M^{φ,ϕ}(\mathbb R^n)$ and obtain the boundedness on $\mathcal M^{φ,ϕ}(\mathbb R^n)$ of the intrinsic Lusin area function $S_α$, the intrinsic $g$-function $g_α$, the intrinsic $g_λ^*$-function $g^\ast_{λ, α}$ and their commutators with ${\rm BMO}(\rn)$ functions, where $α\in(0,1]$, $λ\in(\min\{\max\{3,\,p_1\},3+2\az/n\},\infty)$ and $p_1$ denotes the uniformly upper type index of $\vz$. Let $Φ: [0,\infty)\to[0,\infty)$ be nondecreasing, $Φ(0)=0$, $Φ(t)>0$ when $t>0$, and $\lim_{t\to\infty}Φ(t)=\infty$, $w\in A_\infty(\mathbb R^n)$ and $ϕ: (0,\infty)\to(0,\infty)$ be nonincreasing. The authors also introduce the weighted Orlicz-Morrey space $M_w^{Φ,ϕ}(\mathbb R^n)$ and obtain the boundedness on $M_w^{Φ,ϕ}(\mathbb R^n)$ of the aforementioned intrinsic Littlewood-Paley functions and their commutators with ${\rm BMO}(\rn)$ functions. Finally, for $q\in[1,\fz)$, the boundedness of the aforementioned intrinsic Littlewood-Paley functions on the Musielak Orlicz Campanato space $\mathcal L^{φ,q}(\mathbb R^n)$ is also established.

math.CA↗