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智科眼: 双语看懂新科研
量子物理学 2621
When(When) electrons(电子) that(that) repel(排斥) each other(彼此) are() confined(限制) to(to) a(一个) small() space(空间),(,) they(它们) can(可以) form(形成) an(an) ordered(有序) crystalline state(晶态) known as(被称为) a(一种) Wigner(维格纳) crystal(晶体).(.) Observing(观察) the fragile(脆弱) crystal(晶体) is() tricky(棘手),(,) since(因为) it() requires(需要) extreme conditions(极端条件) including(包括) low temperatures(低温) and() densities(密度),(,) as well as(以及) noninvasive(非侵入性) imaging(成像) probes(探针).(.) To(To) overcome(克服) the challenging(挑战) conditions(条件) of(of) imaging(成像),(,) I(I) .(.) Shapir(Shapir) and() a(a) research(研究) team(小组) in(in) the departments() of(of) Physics(物理) and() Condensed(凝聚) Matter(问题) Physics(物理) in(in) Israel(以色列),(,) Romania(罗马尼亚) and() Hungary(匈牙利) created(创造) conditions() in(in) a(a) carbon() nanotube(纳米管) (NT)((NT)) to(to) house(容纳) the electrons(电子).(.) They(他们) followed(遵循) this() experimental(实验) step(步骤) by(通过) using(使用) a(a) second(第二) nanotube(纳米管) as(as) a(a) probe(探针) ((()called(称为) "(")probe(探针) NT")(NT")) to(to) scan(扫描) the first(第一) nanotube(纳米管) ((()termed(称为) "(")system(系统) NT").(NT").) The physicists(物理学家) measured(测量) the electronic(电子) densities(密度) and() showed(显示) their(它们) consistency(一致性) with(with) theoretical(理论) predictions(预测) to(to) demonstrate(证明) small() Wigner(1-D) crystals(晶体) of(of) up(up) to(to) six() electrons(电子) in(in) one(one) dimension() (1-D).((1-D).) The results(结果) are(are) now(现已) published(发表) in(in) Science(科学).(.)
More(More) than(than) 80(80) years ago(多年前),(,) physicist(物理学家) Eugene(尤金) Wigner(维格纳) predicted(预言) the quantum crystal(量子晶体) of(of) electrons(电子),(,) which(which) remains(仍然) one(之一) of(of) the most() elusive(难以捉摸) states of matter(物质状态).(.) In(In) the present(目前) work(工作),(,) Shapir(Shapir) and() co-(共同)workers(工人) developed(开发) a(一种) technique(技术) to(to) directly(直接) image(成像) the Wigner(维格纳) crystal(晶体) in(in) 1-D(1-D) by(通过) imaging(成像) its(及其) charge density(电荷密度) in(in) real(真实) space(空间).(.) They(他们) obtained(获得) images(图像) of(of) a(a) few(few) electrons(电子) confined(限制) in(in) 1-D(1-D) that(that) matched(匹配) the theoretical(理论) predictions(预测) for(for) strongly() interacting(相互作用) crystals(晶体).(.) The scientists(科学家们) viewed(观察) the quantum(量子) nature() of(of) the crystal(晶体) using() collective(集体) tunneling() through(通过) an(an) electric potential(电势) barrier() confined(限制) with(with) electrically() independent(独立) gates().(.) The work(工作) provided(提供了) direct(直接) evidence(证据) to(to) the formation(形成) of(of) small() Wigner crystals(维格纳晶体),(,) paving(道路) the way(方法) to(to) study(研究) fragile(脆弱) interacting(相互作用) states(状态) of(of) electrons(电子) by(通过) imaging(成像) their(它们) many-body(多体) density(密度) in(in) real(真实) space(空间).(.)
In(In) his() 1934(1934) paper(论文),(,) physicist(物理学家) Eugene(尤金) Wigner(维格纳) predicted(预测) that(that) when(when) long-range(远程) Coulomb interactions(库仑相互作用) in(in) a(a) system(系统) of(of) electrons(电子) dominated(主导) the kinetic energy(动能) and() disorder(无序),(,) they(它们) would() emerge(出现) in(in) a(a) crystalline(晶体) ground state(基态).(.) Where(Where) the electrons(电子) were() kept(保持) apart(分开) irrespective(不论) of(of) their(它们) quantum number(量子数) .(.) Experimental(实验) physicists(物理学家) began(开始) to(to) search(寻找) for(for) this(这种) quantum crystal(量子晶体) in(in) the cleanest(干净) available(可用) electronic(电子) systems(系统中) thereafter(此后),(,) including(包括) liquid helium(液氦) and() low()-()dimensional() semiconductor heterostructures(半导体异质结构).(.)
Physicists(物理学家) had(had) previously(此前曾) conducted(进行) measurements(测量) in(in) two-dimensional(二维) (2-D)((2-D)) electronic(电子) systems(系统中) relative(相对) to(to) transport(传输),(,) microwave(微波) fields(),(,) nuclear magnetic resonance(核磁共振),(,) optical(),(,) tunneling(隧道) and() bilayer(双层) electron(电子) systems(系统) to(to) indicate(指示) the existence(存在) of(of) a(a) crystal(晶体) at(at) high() magnetic fields(磁场).(.) Observing(观察) a(a) crystalline state(晶态) in(in) one(one)-()dimension() (1-D),((1-D),) in(in) an(an) infinite(无限) system(系统) is() unexpected(出乎意料),(,) since(因为) thermal() and() quantum(量子) fluctuations(波动) can() destroy(破坏) long-range order(长程有序).(.) However(然而),(,) in(in) finite(有限) systems(系统中),(,) physicists(物理学家) had() studied(研究了) the theoretical(理论) one-dimensional(一维) Wigner(维格纳) crystal(晶体) state() since(因为) the quasi()-()long-range order(长程有序) produced(产生) crystalline(晶体) correlations(相关性).(.) Experimental(实验) physicists(物理学家) followed(跟随) this(这种) observation(观察结果) with(with) experimental(实验) probing(探测) via(通过) transport(运输) measurements(测量),(,) but() the experiments(实验) could(可能) only(只能) probe(探测) macroscopic(宏观) properties(特性) of(of) this(这一) state(状态).(.)
In(In) principle(原则),(,) a(a) suitable(合适) imaging(成像) tool(工具) is(is) required(需要) to(to) observe(观察) the unambiguous(明确) fingerprint(指纹) of(of) a(a) Wigner(维格纳) crystal(晶体) in(in) its() real(真实)-()space structure(空间结构).(.) Scientists(科学家们) therefore(因此) used(使用) scanning(扫描) probe(探针) experiments(实验),(,) although(尽管) they(他们) could(可能) only(只能) image(成像) the non(non)-()interacting(相互作用) state(状态) or() show(显示) invasive(侵入) gating(门控) by(by) the probe(探针).(.) The measurements(测量) highlighted(突出) the inherent(固有) difficulty(困难) of(of) imaging(成像) electron interactions(电子相互作用) with(with) conventional(传统) scanning(扫描) methods(方法).(.) To(To) individually(单独) resolve(解决) and() identify(识别) electrons(电子),(,) a(a) macroscopic(宏观),(,) metallic(金属) or() dielectric(电介质) tip(尖端) should(应该) approach(接近) the electrons(电子) closer(接近) than(than) their(它们) mutual(相互) separation(分离).(.) Nevertheless(然而),(,) such(such) tips(提示) and() their() interactions(相互作用) can(可能) strongly(强烈) distort(扭曲) the state(状态) being(being) studied(研究).(.) Scientists(科学家) therefore(因此) required(需要) a(一种) different(不同) scanning(扫描) probe(探针) to(to) image(成像) an(an) interacting(相互作用) state(状态) or() electron(电子) system(系统).(.)
In(In) the present(目前) work(工作),(,) Shapir(Shapir) et() al.(al.) introduced(介绍了) a(一种) scanning(扫描) probe(探针) platform(平台) that() used(使用) a(a) carbon() nanotube(纳米管) (NT)((NT)) as(as) a(a) highly sensitive(高灵敏度),(,) yet(然而) minimally(微创) invasive(侵袭) scanning(扫描) probe(探针) to(to) view(观察) the many-body(多体) density(密度) of(of) strongly() interacting(相互作用) electrons(电子).(.) The platform(平台) contained(包含) a(一个) custom(定制)-()made(made) scanning(扫描) probe(探针) microscope(显微镜) operating(工作) at(at) cryogenic(低温) temperatures() (~10((~10) mK)(mK)) where(where) two(两个) opposing(相对) NT(NT) devices(设备) could(可以) be(be) brought(带来) in(in) close(接近) proximity(靠近) and() scanned(扫描) along(along) each other(彼此).(.) The scientists(科学家们) used(使用) one(一个) device(设备) to(to) host([宿]主) the system(系统) NT(NT) as(as) the 1-D(1-D) platform(平台) under(under) study(研究),(,) and() the second(第二) device(设备) perpendicularly(垂直于) to(to) that(那个) to(to) contain(包含) the probe(探针) NT.(NT.) They(他们) assembled(组装) the two(两个) devices(装置) using(使用) a(a) nanoassembly(纳米) technique(技术) to(to) form(形成) pristine(原始) NTs(NT) suspended(悬挂) above(上方) an(an) array(阵列) of(of) metallic(金属) gates().(.)
The scientists(科学家) crucially(至关重要) maintained(保持) strong(强烈) interactions(相互作用) and() low() disorder(无序) in(in) the system(系统) to(to) obtain(获得) a(一个) Wigner(维格纳) crystal(晶体) by(通过) suspending(悬挂) the NTs(NT) far(远远) above(之上) the metallic(金属) gates(栅极) at(at) 400(400) nm(nm) .(.) Then(然后) using(使用) 10(10) electrically() independent(独立) gates(栅极) they(它们) designed(设计了) a(a) potential(电位) that(that) confined(限制) the electrons(电子) between(between) two(两个) barriers(屏障) 1(1) µm(µm) apart(相距),(,) localizing(定位) them(他们) centrally(中心) in(in) a(a) long() suspended(悬浮) nanotube(纳米管),(,) away from(远离) contacts(触点) to(to) prevent(防止) undesirable(不希望) interactions(相互作用).(.)
Shapir(Shapir) et() al.(al.) used(使用) highly(高度) opaque(不透明) barriers(屏障) to(to) prevent(防止) hybridization(杂交) of(of) the confined(受限) electron(电子)'s('s) wave function(波函数) with(with) those(那些) of(of) the electrons(电子) in(in) the rest(其余) of(of) the NT(NT) .(.) Since(由于) transport(传输) in(in) this(这种) situation(情况) was() highly(高度) suppressed(抑制),(,) the scientists(科学家) probed(探测) the confined(受限) electrons(电子) using(使用) a(a) charge(电荷) detector(检测器) located(位于) on(on) a(a) separate(单独) segment() of(of) the same(同一) NT.(NT.) The probe(探针) NT(NT) device(装置) separately(单独) used(使用) in(in) the study(研究) maintained(保持) an(an) almost(几乎) identical(相同) structure(结构),(,) which(which) only() differed(不同) by(通过) the suspension(悬浮) length(长度) of(of) 1.6(1.6) µm(µm) and() the number(数量) of(of) gates() ((()three(三个)).().)
The scientists(科学家们) demonstrated(展示) the working(工作) principle(原理) underlying(潜在) the imaging(成像技术) technique(技术) known as(被称为) the "(")scanning(扫描) charge(电荷),"(,") starting(开始) with(with) the simplest(最简单) experiments(实验) on(on) imaging(成像) the charge distribution(电荷分布) of(of) a(a) single(单个) electron(电子) confined(限制) in(in) a(a) 1-D(1-D) box().(.) Shapir(Shapir) et() al.(al.) measured(测量) the energetic(能量) response(响应) of(of) the system(系统) to(to) a(a) scanned(扫描) perturbation(扰动) ((()agitation(搅动))()) and() directly(直接) determined(确定) the system(系统)'s('s) density distribution(密度分布).(.) By(通过) measuring(测量) the system(系统)'s('s) energy(能量) as(as) a(a) function(函数) of(of) the probe(探头) NT,(NT,) the scientists(科学家们) directly(直接) resolved(解决) the electron(电子)'s('s) density(密度) profile(分布).(.) When(When) measuring(测量) the energy(能量),(,) the scientists(科学家) referenced(引用) it() to(to) the Fermi(费米) energy(能量) in(in) the leads(引线) and() credited(归功于) the perturbation(扰动) produced(产生) by(by) the probes(探针) to(to) the separation(分离) between(between) the two(两个) NTs(NT) and(以及) to(to) the confined(受限) charge(电荷) within(within) the probe(探针) NT.(NT.)
Shapir(Shapir) et() al.(al.) obtained(获得) six() panels(面板) in(in) the experiments(实验) to(to) indicate(指示) the differential(差分) density(密度) of(of) the six() electrons(电子) added(添加) to(to) the system(系统) NT.(NT.) For(For) minimal(最小) perturbations(扰动),(,) they(他们) performed(进行) all(所有) scans(扫描) with(with) one(一个) electron(电子) in(in) the probe(探针) NT.(NT.) The imaged(成像) density(密度) profiles(分布) clearly(明显) differed(不同) from(from) those(那些) predicted(预测) by(by) single()-()particle(粒子) physics(物理) yet() matched(匹配) those(那些) of(of) a(a) strongly() interacting(相互作用) crystal(晶体).(.) When(When) Shapir(Shapir) et() al.(al.) increased(增加) the number(数量) of(of) electrons(电子),(,) the electron(电子) spacing(间距) reduced(减小),(,) although(尽管) their(它们) overall() speed(速度) increased(增加) to(to) signify(表明) electrons(电子) confined(限制) in(in) a(a) "(")box(盒子)"(") with(with) soft() walls().(.) The resulting(得到) images(图像) provided(提供了) direct(直接),(,) real(真实)-()space(空间) observations(观察) of(of) the electronic(电子) Wigner(维格纳) crystals(晶体).(.)
To(To) quantitatively(定量地) understand(理解) the measurements(测量),(,) Shapir(Shapir) et() al.(al.) performed(执行) density matrix(密度矩阵) renormalization(重整化) group(group) (DMRG)((DMRG)) calculations(计算) and() included(包括) long-range(远程) Coulomb interactions(库仑相互作用).(.) The measured(测得) electron(电子) positions(位置) ((()viewed(观察) as(as) green(绿色) stars(恒星))()) agreed(一致) well(well) with(with) those(那些) predicted(预测) by(by) DMRG,(DMRG,) placing() the observed(观察) crystals(晶体) well(well) within(within) the strongly() interacting(相互作用) regime(制度) in(in) the experimental(实验) setup(装置).(.) To(To) understand(理解) the quantum(量子) nature() of(of) the Wigner(维格纳) crystal(晶体),(,) Shapir(Shapir) et() al.(al.) measured(测量) the tunneling(隧道) characteristics(特性) of(of) the crystal(晶体) and() expected(期望) the correlations(相关性) between(between) the electrons(电子) in(in) a(a) crystal(晶体) to(to) cause(原因) the crystal(晶体) to(to) tunnel(隧道) through(through) a(a) barrier(阻挡层) collectively(共同).(.) They(他们) observed(观察) the tunneling(隧道) differential(差分) density(密度) become(变得) more(以上) interesting(有趣) in(in) a(一个) system(系统) with(with) more than(以上) one(one) electron(电子) since(因为) it() displayed(显示) direct(直接) fingerprints(指纹) of(of) collective motion(集体运动).(.)
In(In) this(这种) way(方法),(,) Shapir(Shapir) et() al.(al.) used(使用) a(一种) new() method(方式) to(to) directly(直接) image(成像) the spatial(空间) ordering(排序) of(of) interacting(相互作用) electrons(电子).(.) Based on(基于) the results(结果),(,) they(他们) anticipate(预计) the possibility(有可能) of(of) addressing(解决) additional(额外) basic(基本) questions(问题) related(相关) to(to) the quantum(量子) electronic(电子) crystal(晶体),(,) including(包括) the nature(性质) of(of) its() magnetic(磁性) ordering(排序).(.) The scanning(扫描) platform(平台) developed(开发) by(by) Shapir(Shapir) et() al.(al.) will() allow(允许) further() exploration(探索) of(of) a(a) much(much) wide range(各种) of(of) canonical(典型) interacting(相互作用) electron(电子) states() of(of) matter(物质) that(that) were(were) previously(以前) beyond(beyond) imaging(成像) reach(达到).(.)

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